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• How to Write a Literature Review | Guide, Examples, & Templates

How to Write a Literature Review | Guide, Examples, & Templates

Published on January 2, 2023 by Shona McCombes . Revised on September 11, 2023.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research that you can later apply to your paper, thesis, or dissertation topic .

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates, and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarize sources—it analyzes, synthesizes , and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

What is the purpose of a literature review, examples of literature reviews, step 1 – search for relevant literature, step 2 – evaluate and select sources, step 3 – identify themes, debates, and gaps, step 4 – outline your literature review’s structure, step 5 – write your literature review, free lecture slides, other interesting articles, frequently asked questions, introduction.

• Quick Run-through
• Step 1 & 2

When you write a thesis , dissertation , or research paper , you will likely have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and its scholarly context
• Develop a theoretical framework and methodology for your research
• Position your work in relation to other researchers and theorists
• Show how your research addresses a gap or contributes to a debate
• Evaluate the current state of research and demonstrate your knowledge of the scholarly debates around your topic.

Writing literature reviews is a particularly important skill if you want to apply for graduate school or pursue a career in research. We’ve written a step-by-step guide that you can follow below.

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See an example

Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research problem and questions .

Make a list of keywords

Start by creating a list of keywords related to your research question. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list as you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some useful databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can also use boolean operators to help narrow down your search.

Make sure to read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

You likely won’t be able to read absolutely everything that has been written on your topic, so it will be necessary to evaluate which sources are most relevant to your research question.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models, and methods?
• Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible , and make sure you read any landmark studies and major theories in your field of research.

You can use our template to summarize and evaluate sources you’re thinking about using. Click on either button below to download.

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It is important to keep track of your sources with citations to avoid plagiarism . It can be helpful to make an annotated bibliography , where you compile full citation information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

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To begin organizing your literature review’s argument and structure, be sure you understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly visual platforms like Instagram and Snapchat—this is a gap that you could address in your own research.

There are various approaches to organizing the body of a literature review. Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarizing sources in order.

Try to analyze patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organize your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text , your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, you can follow these tips:

• Summarize and synthesize: give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: don’t just paraphrase other researchers — add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically evaluate: mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: use transition words and topic sentences to draw connections, comparisons and contrasts

In the conclusion, you should summarize the key findings you have taken from the literature and emphasize their significance.

When you’ve finished writing and revising your literature review, don’t forget to proofread thoroughly before submitting. Not a language expert? Check out Scribbr’s professional proofreading services !

This article has been adapted into lecture slides that you can use to teach your students about writing a literature review.

Scribbr slides are free to use, customize, and distribute for educational purposes.

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If you want to know more about the research process , methodology , research bias , or statistics , make sure to check out some of our other articles with explanations and examples.

• Sampling methods
• Simple random sampling
• Stratified sampling
• Cluster sampling
• Likert scales
• Reproducibility

 Statistics

• Null hypothesis
• Statistical power
• Probability distribution
• Effect size
• Poisson distribution

Research bias

• Optimism bias
• Cognitive bias
• Implicit bias
• Hawthorne effect
• Anchoring bias
• Explicit bias

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of credible sources on a topic, often used in dissertations , theses, and research papers . Literature reviews give an overview of knowledge on a subject, helping you identify relevant theories and methods, as well as gaps in existing research. Literature reviews are set up similarly to other  academic texts , with an introduction , a main body, and a conclusion .

An  annotated bibliography is a list of  source references that has a short description (called an annotation ) for each of the sources. It is often assigned as part of the research process for a  paper .  

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Writing a Literature Review

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A literature review is a document or section of a document that collects key sources on a topic and discusses those sources in conversation with each other (also called synthesis ). The lit review is an important genre in many disciplines, not just literature (i.e., the study of works of literature such as novels and plays). When we say “literature review” or refer to “the literature,” we are talking about the research ( scholarship ) in a given field. You will often see the terms “the research,” “the scholarship,” and “the literature” used mostly interchangeably.

Where, when, and why would I write a lit review?

There are a number of different situations where you might write a literature review, each with slightly different expectations; different disciplines, too, have field-specific expectations for what a literature review is and does. For instance, in the humanities, authors might include more overt argumentation and interpretation of source material in their literature reviews, whereas in the sciences, authors are more likely to report study designs and results in their literature reviews; these differences reflect these disciplines’ purposes and conventions in scholarship. You should always look at examples from your own discipline and talk to professors or mentors in your field to be sure you understand your discipline’s conventions, for literature reviews as well as for any other genre.

A literature review can be a part of a research paper or scholarly article, usually falling after the introduction and before the research methods sections. In these cases, the lit review just needs to cover scholarship that is important to the issue you are writing about; sometimes it will also cover key sources that informed your research methodology.

Lit reviews can also be standalone pieces, either as assignments in a class or as publications. In a class, a lit review may be assigned to help students familiarize themselves with a topic and with scholarship in their field, get an idea of the other researchers working on the topic they’re interested in, find gaps in existing research in order to propose new projects, and/or develop a theoretical framework and methodology for later research. As a publication, a lit review usually is meant to help make other scholars’ lives easier by collecting and summarizing, synthesizing, and analyzing existing research on a topic. This can be especially helpful for students or scholars getting into a new research area, or for directing an entire community of scholars toward questions that have not yet been answered.

What are the parts of a lit review?

Most lit reviews use a basic introduction-body-conclusion structure; if your lit review is part of a larger paper, the introduction and conclusion pieces may be just a few sentences while you focus most of your attention on the body. If your lit review is a standalone piece, the introduction and conclusion take up more space and give you a place to discuss your goals, research methods, and conclusions separately from where you discuss the literature itself.

Introduction:

• An introductory paragraph that explains what your working topic and thesis is
• A forecast of key topics or texts that will appear in the review
• Potentially, a description of how you found sources and how you analyzed them for inclusion and discussion in the review (more often found in published, standalone literature reviews than in lit review sections in an article or research paper)
• Summarize and synthesize: Give an overview of the main points of each source and combine them into a coherent whole
• Analyze and interpret: Don’t just paraphrase other researchers – add your own interpretations where possible, discussing the significance of findings in relation to the literature as a whole
• Critically Evaluate: Mention the strengths and weaknesses of your sources
• Write in well-structured paragraphs: Use transition words and topic sentence to draw connections, comparisons, and contrasts.

Conclusion:

• Summarize the key findings you have taken from the literature and emphasize their significance
• Connect it back to your primary research question

How should I organize my lit review?

Lit reviews can take many different organizational patterns depending on what you are trying to accomplish with the review. Here are some examples:

• Chronological : The simplest approach is to trace the development of the topic over time, which helps familiarize the audience with the topic (for instance if you are introducing something that is not commonly known in your field). If you choose this strategy, be careful to avoid simply listing and summarizing sources in order. Try to analyze the patterns, turning points, and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred (as mentioned previously, this may not be appropriate in your discipline — check with a teacher or mentor if you’re unsure).
• Thematic : If you have found some recurring central themes that you will continue working with throughout your piece, you can organize your literature review into subsections that address different aspects of the topic. For example, if you are reviewing literature about women and religion, key themes can include the role of women in churches and the religious attitude towards women.
• Qualitative versus quantitative research
• Empirical versus theoretical scholarship
• Divide the research by sociological, historical, or cultural sources
• Theoretical : In many humanities articles, the literature review is the foundation for the theoretical framework. You can use it to discuss various theories, models, and definitions of key concepts. You can argue for the relevance of a specific theoretical approach or combine various theorical concepts to create a framework for your research.

What are some strategies or tips I can use while writing my lit review?

Any lit review is only as good as the research it discusses; make sure your sources are well-chosen and your research is thorough. Don’t be afraid to do more research if you discover a new thread as you’re writing. More info on the research process is available in our "Conducting Research" resources .

As you’re doing your research, create an annotated bibliography ( see our page on the this type of document ). Much of the information used in an annotated bibliography can be used also in a literature review, so you’ll be not only partially drafting your lit review as you research, but also developing your sense of the larger conversation going on among scholars, professionals, and any other stakeholders in your topic.

Usually you will need to synthesize research rather than just summarizing it. This means drawing connections between sources to create a picture of the scholarly conversation on a topic over time. Many student writers struggle to synthesize because they feel they don’t have anything to add to the scholars they are citing; here are some strategies to help you:

• It often helps to remember that the point of these kinds of syntheses is to show your readers how you understand your research, to help them read the rest of your paper.
• Writing teachers often say synthesis is like hosting a dinner party: imagine all your sources are together in a room, discussing your topic. What are they saying to each other?
• Look at the in-text citations in each paragraph. Are you citing just one source for each paragraph? This usually indicates summary only. When you have multiple sources cited in a paragraph, you are more likely to be synthesizing them (not always, but often
• Read more about synthesis here.

The most interesting literature reviews are often written as arguments (again, as mentioned at the beginning of the page, this is discipline-specific and doesn’t work for all situations). Often, the literature review is where you can establish your research as filling a particular gap or as relevant in a particular way. You have some chance to do this in your introduction in an article, but the literature review section gives a more extended opportunity to establish the conversation in the way you would like your readers to see it. You can choose the intellectual lineage you would like to be part of and whose definitions matter most to your thinking (mostly humanities-specific, but this goes for sciences as well). In addressing these points, you argue for your place in the conversation, which tends to make the lit review more compelling than a simple reporting of other sources.

What is a Literature Review? How to Write It (with Examples)

A literature review is a critical analysis and synthesis of existing research on a particular topic. It provides an overview of the current state of knowledge, identifies gaps, and highlights key findings in the literature. 1 The purpose of a literature review is to situate your own research within the context of existing scholarship, demonstrating your understanding of the topic and showing how your work contributes to the ongoing conversation in the field. Learning how to write a literature review is a critical tool for successful research. Your ability to summarize and synthesize prior research pertaining to a certain topic demonstrates your grasp on the topic of study, and assists in the learning process. 

Table of Contents

What is the purpose of literature review , a. habitat loss and species extinction: , b. range shifts and phenological changes: , c. ocean acidification and coral reefs: , d. adaptive strategies and conservation efforts: .

• Choose a Topic and Define the Research Question: 
• Decide on the Scope of Your Review: 
• Select Databases for Searches: 
• Conduct Searches and Keep Track: 
• Review the Literature: 
• Organize and Write Your Literature Review: 
• How to write a literature review faster with Paperpal? 

Frequently asked questions 

What is a literature review .

A well-conducted literature review demonstrates the researcher’s familiarity with the existing literature, establishes the context for their own research, and contributes to scholarly conversations on the topic. One of the purposes of a literature review is also to help researchers avoid duplicating previous work and ensure that their research is informed by and builds upon the existing body of knowledge.

A literature review serves several important purposes within academic and research contexts. Here are some key objectives and functions of a literature review: 2  

1. Contextualizing the Research Problem: The literature review provides a background and context for the research problem under investigation. It helps to situate the study within the existing body of knowledge. 

2. Identifying Gaps in Knowledge: By identifying gaps, contradictions, or areas requiring further research, the researcher can shape the research question and justify the significance of the study. This is crucial for ensuring that the new research contributes something novel to the field.

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3. Understanding Theoretical and Conceptual Frameworks: Literature reviews help researchers gain an understanding of the theoretical and conceptual frameworks used in previous studies. This aids in the development of a theoretical framework for the current research. 

4. Providing Methodological Insights: Another purpose of literature reviews is that it allows researchers to learn about the methodologies employed in previous studies. This can help in choosing appropriate research methods for the current study and avoiding pitfalls that others may have encountered. 

5. Establishing Credibility: A well-conducted literature review demonstrates the researcher’s familiarity with existing scholarship, establishing their credibility and expertise in the field. It also helps in building a solid foundation for the new research. 

6. Informing Hypotheses or Research Questions: The literature review guides the formulation of hypotheses or research questions by highlighting relevant findings and areas of uncertainty in existing literature. 

Literature review example 

Let’s delve deeper with a literature review example: Let’s say your literature review is about the impact of climate change on biodiversity. You might format your literature review into sections such as the effects of climate change on habitat loss and species extinction, phenological changes, and marine biodiversity. Each section would then summarize and analyze relevant studies in those areas, highlighting key findings and identifying gaps in the research. The review would conclude by emphasizing the need for further research on specific aspects of the relationship between climate change and biodiversity. The following literature review template provides a glimpse into the recommended literature review structure and content, demonstrating how research findings are organized around specific themes within a broader topic. 

Literature Review on Climate Change Impacts on Biodiversity:  

Climate change is a global phenomenon with far-reaching consequences, including significant impacts on biodiversity. This literature review synthesizes key findings from various studies: 

Climate change-induced alterations in temperature and precipitation patterns contribute to habitat loss, affecting numerous species (Thomas et al., 2004). The review discusses how these changes increase the risk of extinction, particularly for species with specific habitat requirements. 

Observations of range shifts and changes in the timing of biological events (phenology) are documented in response to changing climatic conditions (Parmesan & Yohe, 2003). These shifts affect ecosystems and may lead to mismatches between species and their resources. 

The review explores the impact of climate change on marine biodiversity, emphasizing ocean acidification’s threat to coral reefs (Hoegh-Guldberg et al., 2007). Changes in pH levels negatively affect coral calcification, disrupting the delicate balance of marine ecosystems. 

Recognizing the urgency of the situation, the literature review discusses various adaptive strategies adopted by species and conservation efforts aimed at mitigating the impacts of climate change on biodiversity (Hannah et al., 2007). It emphasizes the importance of interdisciplinary approaches for effective conservation planning. 

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How to write a good literature review 

Writing a literature review involves summarizing and synthesizing existing research on a particular topic. A good literature review format should include the following elements. 

Introduction: The introduction sets the stage for your literature review, providing context and introducing the main focus of your review. 

• Opening Statement: Begin with a general statement about the broader topic and its significance in the field. 
• Scope and Purpose: Clearly define the scope of your literature review. Explain the specific research question or objective you aim to address. 
• Organizational Framework: Briefly outline the structure of your literature review, indicating how you will categorize and discuss the existing research. 
• Significance of the Study: Highlight why your literature review is important and how it contributes to the understanding of the chosen topic. 
• Thesis Statement: Conclude the introduction with a concise thesis statement that outlines the main argument or perspective you will develop in the body of the literature review. 

Body: The body of the literature review is where you provide a comprehensive analysis of existing literature, grouping studies based on themes, methodologies, or other relevant criteria. 

• Organize by Theme or Concept: Group studies that share common themes, concepts, or methodologies. Discuss each theme or concept in detail, summarizing key findings and identifying gaps or areas of disagreement. 
• Critical Analysis: Evaluate the strengths and weaknesses of each study. Discuss the methodologies used, the quality of evidence, and the overall contribution of each work to the understanding of the topic. 
• Synthesis of Findings: Synthesize the information from different studies to highlight trends, patterns, or areas of consensus in the literature. 
• Identification of Gaps: Discuss any gaps or limitations in the existing research and explain how your review contributes to filling these gaps. 
• Transition between Sections: Provide smooth transitions between different themes or concepts to maintain the flow of your literature review. 

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Conclusion: The conclusion of your literature review should summarize the main findings, highlight the contributions of the review, and suggest avenues for future research. 

• Summary of Key Findings: Recap the main findings from the literature and restate how they contribute to your research question or objective. 
• Contributions to the Field: Discuss the overall contribution of your literature review to the existing knowledge in the field. 
• Implications and Applications: Explore the practical implications of the findings and suggest how they might impact future research or practice. 
• Recommendations for Future Research: Identify areas that require further investigation and propose potential directions for future research in the field. 
• Final Thoughts: Conclude with a final reflection on the importance of your literature review and its relevance to the broader academic community. 

Conducting a literature review 

Conducting a literature review is an essential step in research that involves reviewing and analyzing existing literature on a specific topic. It’s important to know how to do a literature review effectively, so here are the steps to follow: 1  

Choose a Topic and Define the Research Question:  

• Select a topic that is relevant to your field of study. 
• Clearly define your research question or objective. Determine what specific aspect of the topic do you want to explore? 

Decide on the Scope of Your Review:  

• Determine the timeframe for your literature review. Are you focusing on recent developments, or do you want a historical overview? 
• Consider the geographical scope. Is your review global, or are you focusing on a specific region? 
• Define the inclusion and exclusion criteria. What types of sources will you include? Are there specific types of studies or publications you will exclude? 

Select Databases for Searches:  

• Identify relevant databases for your field. Examples include PubMed, IEEE Xplore, Scopus, Web of Science, and Google Scholar. 
• Consider searching in library catalogs, institutional repositories, and specialized databases related to your topic. 

Conduct Searches and Keep Track:  

• Develop a systematic search strategy using keywords, Boolean operators (AND, OR, NOT), and other search techniques. 
• Record and document your search strategy for transparency and replicability. 
• Keep track of the articles, including publication details, abstracts, and links. Use citation management tools like EndNote, Zotero, or Mendeley to organize your references. 

Review the Literature:  

• Evaluate the relevance and quality of each source. Consider the methodology, sample size, and results of studies. 
• Organize the literature by themes or key concepts. Identify patterns, trends, and gaps in the existing research. 
• Summarize key findings and arguments from each source. Compare and contrast different perspectives. 
• Identify areas where there is a consensus in the literature and where there are conflicting opinions. 
• Provide critical analysis and synthesis of the literature. What are the strengths and weaknesses of existing research? 

Organize and Write Your Literature Review:  

• Literature review outline should be based on themes, chronological order, or methodological approaches. 
• Write a clear and coherent narrative that synthesizes the information gathered. 
• Use proper citations for each source and ensure consistency in your citation style (APA, MLA, Chicago, etc.). 
• Conclude your literature review by summarizing key findings, identifying gaps, and suggesting areas for future research. 

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How to write a literature review faster with Paperpal?  

Paperpal, an AI writing assistant, integrates powerful academic search capabilities within its writing platform. With the Research | Cite feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface. It also allows you auto-cite references in 10,000+ styles and save relevant references in your Citation Library. By eliminating the need to switch tabs to find answers to all your research questions, Paperpal saves time and helps you stay focused on your writing.   

Here’s how to use the Research feature:  

• Ask a question: Get started with a new document on paperpal.com. Click on the “Research | Cite” feature and type your question in plain English. Paperpal will scour over 250 million research articles, including conference papers and preprints, to provide you with accurate insights and citations. 

• Review and Save: Paperpal summarizes the information, while citing sources and listing relevant reads. You can quickly scan the results to identify relevant references and save these directly to your built-in citations library for later access. 
• Cite with Confidence: Paperpal makes it easy to incorporate relevant citations and references in 10,000+ styles into your writing, ensuring your arguments are well-supported by credible sources. This translates to a polished, well-researched literature review. 

The literature review sample and detailed advice on writing and conducting a review will help you produce a well-structured report. But remember that a good literature review is an ongoing process, and it may be necessary to revisit and update it as your research progresses. By combining effortless research with an easy citation process, Paperpal Research streamlines the literature review process and empowers you to write faster and with more confidence. Try Paperpal Research now and see for yourself.  

A literature review is a critical and comprehensive analysis of existing literature (published and unpublished works) on a specific topic or research question and provides a synthesis of the current state of knowledge in a particular field. A well-conducted literature review is crucial for researchers to build upon existing knowledge, avoid duplication of efforts, and contribute to the advancement of their field. It also helps researchers situate their work within a broader context and facilitates the development of a sound theoretical and conceptual framework for their studies.

Literature review is a crucial component of research writing, providing a solid background for a research paper’s investigation. The aim is to keep professionals up to date by providing an understanding of ongoing developments within a specific field, including research methods, and experimental techniques used in that field, and present that knowledge in the form of a written report. Also, the depth and breadth of the literature review emphasizes the credibility of the scholar in his or her field.  

Before writing a literature review, it’s essential to undertake several preparatory steps to ensure that your review is well-researched, organized, and focused. This includes choosing a topic of general interest to you and doing exploratory research on that topic, writing an annotated bibliography, and noting major points, especially those that relate to the position you have taken on the topic. 

Literature reviews and academic research papers are essential components of scholarly work but serve different purposes within the academic realm. 3 A literature review aims to provide a foundation for understanding the current state of research on a particular topic, identify gaps or controversies, and lay the groundwork for future research. Therefore, it draws heavily from existing academic sources, including books, journal articles, and other scholarly publications. In contrast, an academic research paper aims to present new knowledge, contribute to the academic discourse, and advance the understanding of a specific research question. Therefore, it involves a mix of existing literature (in the introduction and literature review sections) and original data or findings obtained through research methods. 

Literature reviews are essential components of academic and research papers, and various strategies can be employed to conduct them effectively. If you want to know how to write a literature review for a research paper, here are four common approaches that are often used by researchers.  Chronological Review: This strategy involves organizing the literature based on the chronological order of publication. It helps to trace the development of a topic over time, showing how ideas, theories, and research have evolved.  Thematic Review: Thematic reviews focus on identifying and analyzing themes or topics that cut across different studies. Instead of organizing the literature chronologically, it is grouped by key themes or concepts, allowing for a comprehensive exploration of various aspects of the topic.  Methodological Review: This strategy involves organizing the literature based on the research methods employed in different studies. It helps to highlight the strengths and weaknesses of various methodologies and allows the reader to evaluate the reliability and validity of the research findings.  Theoretical Review: A theoretical review examines the literature based on the theoretical frameworks used in different studies. This approach helps to identify the key theories that have been applied to the topic and assess their contributions to the understanding of the subject.  It’s important to note that these strategies are not mutually exclusive, and a literature review may combine elements of more than one approach. The choice of strategy depends on the research question, the nature of the literature available, and the goals of the review. Additionally, other strategies, such as integrative reviews or systematic reviews, may be employed depending on the specific requirements of the research.

The literature review format can vary depending on the specific publication guidelines. However, there are some common elements and structures that are often followed. Here is a general guideline for the format of a literature review:  Introduction:   Provide an overview of the topic.  Define the scope and purpose of the literature review.  State the research question or objective.  Body:   Organize the literature by themes, concepts, or chronology.  Critically analyze and evaluate each source.  Discuss the strengths and weaknesses of the studies.  Highlight any methodological limitations or biases.  Identify patterns, connections, or contradictions in the existing research.  Conclusion:   Summarize the key points discussed in the literature review.  Highlight the research gap.  Address the research question or objective stated in the introduction.  Highlight the contributions of the review and suggest directions for future research.

Both annotated bibliographies and literature reviews involve the examination of scholarly sources. While annotated bibliographies focus on individual sources with brief annotations, literature reviews provide a more in-depth, integrated, and comprehensive analysis of existing literature on a specific topic. The key differences are as follows: 

References 

• Denney, A. S., & Tewksbury, R. (2013). How to write a literature review.  Journal of criminal justice education ,  24 (2), 218-234. 
• Pan, M. L. (2016).  Preparing literature reviews: Qualitative and quantitative approaches . Taylor & Francis. 
• Cantero, C. (2019). How to write a literature review.  San José State University Writing Center . 

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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

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1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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• Introduction

Literature Review: The What, Why and How-to Guide — Introduction

• Getting Started
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What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

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What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

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For help, please contact the librarian for your subject area.  We have a guide to library specialists by subject .

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What is a Literature Review? | Guide, Template, & Examples

Published on 22 February 2022 by Shona McCombes . Revised on 7 June 2022.

What is a literature review? A literature review is a survey of scholarly sources on a specific topic. It provides an overview of current knowledge, allowing you to identify relevant theories, methods, and gaps in the existing research.

There are five key steps to writing a literature review:

• Search for relevant literature
• Evaluate sources
• Identify themes, debates and gaps
• Outline the structure
• Write your literature review

A good literature review doesn’t just summarise sources – it analyses, synthesises, and critically evaluates to give a clear picture of the state of knowledge on the subject.

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Table of contents

Why write a literature review, examples of literature reviews, step 1: search for relevant literature, step 2: evaluate and select sources, step 3: identify themes, debates and gaps, step 4: outline your literature review’s structure, step 5: write your literature review, frequently asked questions about literature reviews, introduction.

• Quick Run-through
• Step 1 & 2

When you write a dissertation or thesis, you will have to conduct a literature review to situate your research within existing knowledge. The literature review gives you a chance to:

• Demonstrate your familiarity with the topic and scholarly context
• Develop a theoretical framework and methodology for your research
• Position yourself in relation to other researchers and theorists
• Show how your dissertation addresses a gap or contributes to a debate

You might also have to write a literature review as a stand-alone assignment. In this case, the purpose is to evaluate the current state of research and demonstrate your knowledge of scholarly debates around a topic.

The content will look slightly different in each case, but the process of conducting a literature review follows the same steps. We’ve written a step-by-step guide that you can follow below.

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Writing literature reviews can be quite challenging! A good starting point could be to look at some examples, depending on what kind of literature review you’d like to write.

• Example literature review #1: “Why Do People Migrate? A Review of the Theoretical Literature” ( Theoretical literature review about the development of economic migration theory from the 1950s to today.)
• Example literature review #2: “Literature review as a research methodology: An overview and guidelines” ( Methodological literature review about interdisciplinary knowledge acquisition and production.)
• Example literature review #3: “The Use of Technology in English Language Learning: A Literature Review” ( Thematic literature review about the effects of technology on language acquisition.)
• Example literature review #4: “Learners’ Listening Comprehension Difficulties in English Language Learning: A Literature Review” ( Chronological literature review about how the concept of listening skills has changed over time.)

You can also check out our templates with literature review examples and sample outlines at the links below.

Download Word doc Download Google doc

Before you begin searching for literature, you need a clearly defined topic .

If you are writing the literature review section of a dissertation or research paper, you will search for literature related to your research objectives and questions .

If you are writing a literature review as a stand-alone assignment, you will have to choose a focus and develop a central question to direct your search. Unlike a dissertation research question, this question has to be answerable without collecting original data. You should be able to answer it based only on a review of existing publications.

Make a list of keywords

Start by creating a list of keywords related to your research topic. Include each of the key concepts or variables you’re interested in, and list any synonyms and related terms. You can add to this list if you discover new keywords in the process of your literature search.

• Social media, Facebook, Instagram, Twitter, Snapchat, TikTok
• Body image, self-perception, self-esteem, mental health
• Generation Z, teenagers, adolescents, youth

Search for relevant sources

Use your keywords to begin searching for sources. Some databases to search for journals and articles include:

• Your university’s library catalogue
• Google Scholar
• Project Muse (humanities and social sciences)
• Medline (life sciences and biomedicine)
• EconLit (economics)
• Inspec (physics, engineering and computer science)

You can use boolean operators to help narrow down your search:

Read the abstract to find out whether an article is relevant to your question. When you find a useful book or article, you can check the bibliography to find other relevant sources.

To identify the most important publications on your topic, take note of recurring citations. If the same authors, books or articles keep appearing in your reading, make sure to seek them out.

You probably won’t be able to read absolutely everything that has been written on the topic – you’ll have to evaluate which sources are most relevant to your questions.

For each publication, ask yourself:

• What question or problem is the author addressing?
• What are the key concepts and how are they defined?
• What are the key theories, models and methods? Does the research use established frameworks or take an innovative approach?
• What are the results and conclusions of the study?
• How does the publication relate to other literature in the field? Does it confirm, add to, or challenge established knowledge?
• How does the publication contribute to your understanding of the topic? What are its key insights and arguments?
• What are the strengths and weaknesses of the research?

Make sure the sources you use are credible, and make sure you read any landmark studies and major theories in your field of research.

You can find out how many times an article has been cited on Google Scholar – a high citation count means the article has been influential in the field, and should certainly be included in your literature review.

The scope of your review will depend on your topic and discipline: in the sciences you usually only review recent literature, but in the humanities you might take a long historical perspective (for example, to trace how a concept has changed in meaning over time).

Remember that you can use our template to summarise and evaluate sources you’re thinking about using!

Take notes and cite your sources

As you read, you should also begin the writing process. Take notes that you can later incorporate into the text of your literature review.

It’s important to keep track of your sources with references to avoid plagiarism . It can be helpful to make an annotated bibliography, where you compile full reference information and write a paragraph of summary and analysis for each source. This helps you remember what you read and saves time later in the process.

You can use our free APA Reference Generator for quick, correct, consistent citations.

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To begin organising your literature review’s argument and structure, you need to understand the connections and relationships between the sources you’ve read. Based on your reading and notes, you can look for:

• Trends and patterns (in theory, method or results): do certain approaches become more or less popular over time?
• Themes: what questions or concepts recur across the literature?
• Debates, conflicts and contradictions: where do sources disagree?
• Pivotal publications: are there any influential theories or studies that changed the direction of the field?
• Gaps: what is missing from the literature? Are there weaknesses that need to be addressed?

This step will help you work out the structure of your literature review and (if applicable) show how your own research will contribute to existing knowledge.

• Most research has focused on young women.
• There is an increasing interest in the visual aspects of social media.
• But there is still a lack of robust research on highly-visual platforms like Instagram and Snapchat – this is a gap that you could address in your own research.

There are various approaches to organising the body of a literature review. You should have a rough idea of your strategy before you start writing.

Depending on the length of your literature review, you can combine several of these strategies (for example, your overall structure might be thematic, but each theme is discussed chronologically).

Chronological

The simplest approach is to trace the development of the topic over time. However, if you choose this strategy, be careful to avoid simply listing and summarising sources in order.

Try to analyse patterns, turning points and key debates that have shaped the direction of the field. Give your interpretation of how and why certain developments occurred.

If you have found some recurring central themes, you can organise your literature review into subsections that address different aspects of the topic.

For example, if you are reviewing literature about inequalities in migrant health outcomes, key themes might include healthcare policy, language barriers, cultural attitudes, legal status, and economic access.

Methodological

If you draw your sources from different disciplines or fields that use a variety of research methods , you might want to compare the results and conclusions that emerge from different approaches. For example:

• Look at what results have emerged in qualitative versus quantitative research
• Discuss how the topic has been approached by empirical versus theoretical scholarship
• Divide the literature into sociological, historical, and cultural sources

Theoretical

A literature review is often the foundation for a theoretical framework . You can use it to discuss various theories, models, and definitions of key concepts.

You might argue for the relevance of a specific theoretical approach, or combine various theoretical concepts to create a framework for your research.

Like any other academic text, your literature review should have an introduction , a main body, and a conclusion . What you include in each depends on the objective of your literature review.

The introduction should clearly establish the focus and purpose of the literature review.

If you are writing the literature review as part of your dissertation or thesis, reiterate your central problem or research question and give a brief summary of the scholarly context. You can emphasise the timeliness of the topic (“many recent studies have focused on the problem of x”) or highlight a gap in the literature (“while there has been much research on x, few researchers have taken y into consideration”).

Depending on the length of your literature review, you might want to divide the body into subsections. You can use a subheading for each theme, time period, or methodological approach.

As you write, make sure to follow these tips:

• Summarise and synthesise: give an overview of the main points of each source and combine them into a coherent whole.
• Analyse and interpret: don’t just paraphrase other researchers – add your own interpretations, discussing the significance of findings in relation to the literature as a whole.
• Critically evaluate: mention the strengths and weaknesses of your sources.
• Write in well-structured paragraphs: use transitions and topic sentences to draw connections, comparisons and contrasts.

In the conclusion, you should summarise the key findings you have taken from the literature and emphasise their significance.

If the literature review is part of your dissertation or thesis, reiterate how your research addresses gaps and contributes new knowledge, or discuss how you have drawn on existing theories and methods to build a framework for your research. This can lead directly into your methodology section.

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a dissertation , thesis, research paper , or proposal .

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarise yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

The literature review usually comes near the beginning of your  dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

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3 Literature Review

Charitianne Williams

By the end of this chapter, you will be able to do the following:

• Understand the purpose and function of a literature review.
• Structure a literature review according to basic genre expectations.
• Synthesize ideas from multiple sources using a synthesis matrix.
• Choose between narrative or parenthetical citation and direct quoting, or paraphrase with intent and purpose.

I. Introduction

The purpose of a literature review is just that—it reviews. This means that literature reviews examine a text after it was produced, with all the benefits that hindsight allows a reader. In popular culture, we commonly review movies, restaurants, vacation spots, products, etc. In those reviews, you look back at the single thing you are reviewing and your experience with it. You focus on the strengths and weaknesses of your experience and judge the experience as positive or negative while recommending or not recommending the place or product and explaining why.

An academic literature review does something different, although some of the skills and strategies you use remain the same. The job of a literature review is to examine a collection of research or scholarship (not a single thing or text) on a given topic and show how that scholarship fits together. Literature reviews summarize, describe, evaluate, and synthesize the work of other authors and researchers while looking for common trends/patterns, themes, inconsistencies, and gaps in this previous research. The main strategy writers of a literature review use is synthesis.

SYNTHESIS: the combination of ideas and elements to form a complete system or theory.

A good metaphor for synthesis is cooking! Imagine the ingredients for a loaf of bread laid out on a kitchen cabinet. Each ingredient—eggs, milk, flour, sugar, salt, yeast—have their own purpose and can be combined in different ways to form food other than bread. Knowing all of those individual attributes that make an egg an egg, or the difference between yeast and flour, is what makes you a chef. When you combine all these ingredients according to the recipe, you get something different than all the ingredients on their own: and most of us would rather eat a slice of bread than a spoonful of flour. The product of synthesis is like bread. Synthesis takes a list of ingredients and makes them into something more than the ingredients alone.

Usually, the writers of a literature review will start with a question that they want to answer through informed and research-based evidence gathered while reading others’ work on related topics. The “thesis” or controlling idea of a literature review may be that same question ( “This review seeks to answer…” ) or it may be a statement describing the reviewed research. The thesis reflects the purpose of the literature review as a genre and is different from the thesis you will write for the research paper that argues a claim or asserts a new idea.

Example 3.1: Look at this thesis statement taken from the introduction of a literature review in environmental psychology on the relationship between “nature sounds” and restorative environments:

From this example, we can learn many things about literature reviews:

• They are explicit and focused on their topic. The opening states an observable truth about the current research ( emphasizes nature ), is followed by a general condition ( positive psychological experiences) within that research, and then finally focuses on describing how a particular outcome is achieved (listening to nature sounds is restorative).
• They seek to pre vent or eliminate misunderstanding. Note the use of specialized key terms, exacting transitional phrases, and meaningful verbs in the thesis such as “ restorative environments,” “in particular,” and “ generate .”
• They seek to forward understanding. In other words, literature reviews examine and link together evidence described and validated in the research of others so a reader can learn how a field is developing. ( Research seems to agree that nature sounds can relieve stress and fatigue–this review will examine that conclusion so readers can understand/ build on how and why.)

Moving from the beginning to the very end of the literature review, we can also learn many things about literature reviews from the sources used. Think of each text listed in the References section of a literature review as contributing pieces to a gigantic puzzle.

Example 3.2: Look at the first three articles listed in the References for the article excerpted above:

Abbott, L. C., Taff, D., Newman, P., Benfield, J. A., and Mowen, A. J. (2016). The influence of natural sounds on attention restoration. J. Park Recreation Adm. 34, 5–15. doi: 10.18666/JPRA-2016-V34-I3-6893

Aletta, F., and Kang, J. (2019). Promoting healthy and supportive acoustic environments: going beyond the quietness. Int. J. Environ. Res. Public Health 16:4988. doi: 10.3390/ijerph16244988

Aletta, F., Oberman, T., and Kang, J. (2018). Associations between positive health-related effects and soundscapes perceptual constructs: a systematic review. Int. J. Environ. Res. Public Health 15:2392. doi: 10.3390/ijerph15112392

None of these sources are exactly the same. One focuses on sound and attention, the next two on sound and health, and none of them are quite the same as sound and restoration —but they are all pieces of the puzzle that give a full understanding of how sound and restorative environments relate.

As the author of the literature review, it is your job to join the pieces together, giving your reader a complete picture of what researchers know about your topic.

Literature reviews are an indispensable tool for researchers. Instead of having to read dozens of articles on a topic, a researcher could instead read a literature review that synthesizes what is known and puts each piece of scholarship into conversation with the others. This could be not only quicker, but also more valuable.

Have you heard the saying that the whole is more than the sum of its parts? The knowledge constructed by a well-written literature review often outweighs the knowledge constructed by simply reading each article in the References section on its own because the author of a literature review processes and analyzes the information for the reader.

Literature reviews occur in two general forms—as a background section in a scholarly work or as a stand-alone genre in and of itself. In both situations, the basic purpose and structure of the literature review is similar: it is the length and the scope that varies. For example, consider the previous chapter, the Proposal. In most proposals, you will want to convince your audience that you are informed on the background of your topic—a literature review is how you would do that. Since a proposal is commonly a short text, you do not have the space to summarize every piece of research. You must select an important set and synthesize that information into a small section signaling your expertise.

On the other hand, consider a professional journal intended to keep its readers up to date on new technologies and findings in a specific field or career. New ideas and discoveries are emerging every day, and it can be difficult to stay on top of all of these new findings, understand how they fit together, and also keep track of your own career responsibilities! A magazine might hire an author to read all the new research on a specific topic and synthesize it into a single article, a state-of-the-art review, so that practitioners in a field can read a single 25-page article instead of 100 25-page articles.

More Resources 3.1: Literature Reviews

II. Rhetorical Considerations: Voice

Using the scholarship of other writers and researchers is one of the things that differentiates academic writing from other types of writing. Using others’ scholarship in a meaningful way that creates new knowledge without mischaracterizing the original findings takes effort, attention, and usually several rounds of revision and rewriting. One of the issues is voice , which refers to the attitude and tone of a text—think of it as what the text “sounds like” in your head as you read it. Voice is an important element of cohesion , or what some people think of as “flow.” Creating a consistent voice in the mind of your reader helps them fit all the information in a text together in the way the author intends. Check out this advice from APAstyle.org about academic style and voice.

Think back to your annotated bibliography and how you created your summaries. You probably used key terms from the original authors’ texts, but because you had to take whole articles and restate the meaning in a short paragraph, there wasn’t room to just repeat the words of the original author. So you had to write the summaries in your voice . If you used those key terms correctly and in ways similar to original authors, those key terms probably did not interfere with cohesiveness and voice. However, in the literature review, you have many more voices to synthesize than you did to summarize in the annotated bibliography. Maintaining a consistent and cohesive voice will be challenging. An important way to maintain voice is through paraphrasing, discussed later in this chapter.

More Resources 3.2: Transitions

Another important way to maintain cohesion is through the use of metadiscourse (see Chapter 2) and transitional phrases. See this link for the use and meaning of transitional phrases, sometimes called signposts .

III. The Literature Review Across the Disciplines

Example 3.3: Academic and Professional Examples

Structure of Literature Reviews

While the details vary across disciplines, all literature reviews tend to have similar basic structure. The introduction of a literature review informs the reader on the topic by defining key terms, citing key researchers or research periods in the field, and introducing the main focus of the review in a descriptive thesis statement. The introduction also explains the organization of the review. In a literature review, you organize your discussion of the research by topic or theme— not article or author. This is in direct contrast to the annotated bibliography, which is often the first step in the writing process for a literature review.

In the annotated bibliography, you organize your entries in alphabetical order by authors’ last names. Each annotation is directly connected to a single text. A literature review is connected to a collection of texts, and therefore must be organized in a way that reflects this.

Example 3.4: Let’s examine the full paragraph that the thesis statement we analyzed earlier came from:

A systematic review by Aletta et al. (2018) has identified links between positive urban soundscapes (which may also include nature sounds) and health and well-being, including stress recovery. Given the emphasis on nature w ithin restorative environments (see Hartig et al., 2014 ), the present narrative literature review focuses on evidence for positive psychological experiences of nature sounds and soundscapes specifically, and in particular how listening to these can generate perceptions and outcomes of restoration from stress and fatigue. This review has five key objectives, summarized in Figure 1 [in the article] . First, it explores literature regarding the impact of nature sounds on perceptions and experiences of wider natural environments. Second, it examines evidence regarding cognitive and affective appraisals of nature sounds and their contributions to overall perceptions of restorative environments. Third, literature regarding restorative outcomes in response to nature sounds is assessed. Fourth, the relevance of key restoration theories to this top ic is examined and areas where these theories are limited are identified. Fifth, a possible new theoretical area of interest—semantic associations with nature—is discussed and exemplified by recent acoustics research (Ratcliffe, 2021, emphasis added).

Notice how the thesis statement (in bold ) is followed by an explicit description of the five key objectives—which correspond to the titles (usually called headings ) of the five major sections of the body of the literature review. The introduction basically outlines the body of the literature review to make it easier for a researcher to find the specific information they are looking for. What follows each of these headings is an analysis and synthesis of the topic described in the heading—which is what we mean when we say a literature review is organized by topic.

Example 3.5: See how the body sections of a literature review synthesize research and evidence in relation to a focused topic. Read this example taken from a literature review in another discipline, nursing.

The introduction states that the review’s purpose is to understand the issues facing nurses in situations such as the COVID-19 pandemic. The researchers found several themes in the research that all contributed to nurses’ experiences. This paragraph describes one of those themes which the authors label “Professional collegiality”:

3.2.2. Professional collegiality

Professional camaraderie amongst nursing colleagues working during a pandemic was high (Ives et al., 2009, Kim, 2018, Liu a nd Liehr , 2009). Nurses acknowledged the importance of caring for their co-workers and in sharing the load. Some nurses associated the experience with working on a battlefield, whereby they worked together as a team protecting one another (Chung et al., 20 05, Kang et al., 2018, Liu and Liehr , 2009). Appreciation of their nursing colleagues was demonstrated through sharing their experiences, willingness to work together and encouraging a team spirit (Shih et al., 2007, Chung et al., 2005, Chiang et al., 2007 ). (Ratcliffe, 2021, p.4)

In this single paragraph, there are seven different research articles cited, and some of them are cited twice. There is no way to write a coherent paragraph summarizing seven different research articles at once—instead, the authors of this paragraph reviewed what the researchers said about collegiality, found where their findings pointed in the same direction, and put those connections into their own words. This is the importance of the review’s body section: it is here where you really dig into the content, meaning, and implications of the scholarship you are discussing.

The end of a literature review looks different from the one- or two-paragraph conclusion we are used to in other texts. The end is often made up of multiple sections, each with a slightly different purpose, although all are probably recognizable to you. A “Discussion” section is almost always present, where the author summarizes the most important findings of each section. In most cases, the “Discussion” section does not contain new information, but ties the different body sections together in ways that provide a deeper analysis.

The end of a literature review may also contain an “Implications for Future Research” or “Resolution” after the Discussion—sometimes this final section is even called “Conclusion.” What this last section looks like is often dependent upon the type of review you are writing, and whether the review is standing alone as a complete text or part of a larger project.

In any situation, across all disciplines, it is important to understand how your literature review is meant to inform the reader and what kind of review is appropriate for the context, in order to decide how you should structure the beginning and end of your review.

Types of Literature Reviews

There are different types of literature reviews, although in undergraduate study the Traditional or Narrative Review is most common. Narrative reviews are somewhat exploratory in their content—in a narrative review you are synthesizing the results of specific texts selected for their connection to your topic. Narrative reviews almost always end with a section describing areas for future research if they are a stand-alone text, or a section describing why the author’s research is so needed if part of a larger research article. The chart below outlines the key differences between three major literature review types. Notice that each type has a slightly different purpose. You might think about which type best fits your project as you read.

Table 3.1: Types of Literature Reviews

More Resources 3.3: Literature Review Structures

IV. Research Strategies: Developing a Methodology

Systematic and scoping reviews should always contain a Research Methodology that explains to your reader exactly how you found the research you are reviewing. Often Narrative Reviews will also contain a research methodology, although it will be slightly different since they are not comprehensive reviews, meaning, they do not attempt to find all the research on a topic—by design, they cover only a specific portion. Even if you are not required to write up your methodology, you need clear research strategies to find the appropriate scholarship for your literature review.

Example 3.6: Check out this excerpt from the methods sections from a psychology literature review. Note how the authors clearly describe what types of sources they’ll be using as well as their steps throughout the research process.

Drawing on individual case studies, archival reports, correlational studies, and laboratory and field experiments, this monograph scrutinizes a sequence of events during which confessions may be obtained from criminal suspects and used as evidence. First, we examine the pre-interrogation interview, a process by which police …( Kassin and Gudjonsson , 2004, p.33)

Example 3.7: Here is another example from the field of education. In it the authors describe two separate searches they performed to gather the literature—the first search used key terms they decided upon before reading any scholarship, and the second search used the terms that they found were common to that first set of texts (see more about key terms here and in the Annotated Bibliography chapter).

We conducted two rounds of literature searches, utilizing the following databases: World CAT (general search), EB SCO Academic Search Complete, EBSCO Education Source, and Linguistics and Language Behavior Abstracts (ProQuest). In the first round, we searched using every possible combination of the following terms: ‘race,’ ‘language teaching,’ ‘ethnicity,’ ‘language p edagogy,’ ‘Whiteness,’ ‘racialized,’ ‘antiracism,’ and ‘ nativeness .’ For the second round of our literature search, we searched using terms that we saw emerging from the literature such as ‘racial identities of language learners,’ ‘racial identities of lan guage teachers,’ ‘language varieties and language teaching,’ ‘race and language teacher education,’ ‘race and educational policy,’ ‘race and language programs,’ and ‘race and language curriculum’ and also repeated our earlier searches in order to keep the literature updated. (Von Esch et al., 2020, p. 392)

No matter the type of research (see a description of qualitative vs. quantitative research ), the specific genres (see descriptions of academic research genres ), or the time frame (see a discussion on the importance of publication date ) you use for your review, it is important to think through the options, make a decision, and incorporate all your research knowledge—use of key terms, use of subject filters, use of specialized databases, etc.—into a coherent and meaningful process that results in the best scholarship for your inquiry and review.

Here’s a video to help you get started on using databases for research:

Library Referral: Connecting the Conversation with Scholarly Sources and Beyond​

(by Annie R. Armstrong)

Research involves drawing from numerous voices from a range of source types. The sources you choose to include in your conversation are context-specific and might vary depending on your topic or the parameters of your assignment. Review your assignment description and talk to your instructor about guidelines. While most research papers emphasize scholarly sources, expertise isn’t always equated with scholarliness and you might want to branch out. For example, a research paper focusing on exploitation of Native American land and communities by the mining industry should make some attempt to include sources generated by the communities under discussion, especially if their point of view is not represented in the peer-reviewed, scholarly sources you’ve found. Think about who the stakeholders are as related to various aspects of your topic and how you can tap into their voices through available resources. You may want to consult a librarian about this.

The chart below summarizes the breadth of source types available through library websites versus the open web:

Table 3.2: Scholarly Sources and Beyond

V. Reading Strategies: Intertextuality and Graphic Organizers

Typically we think of reading as something we do to learn the content of a text—and this is absolutely true! But true understanding means knowing the relationships between and impact of separate but related topics, which might mean understanding how different texts—generally focused on one topic—overlap or differ.

Intertextuality refers to the connections that exist between texts. Intertextuality as a reading strategy means looking for the connections between the text you are reading and others you have already read; anticipating connections with other texts that you have not yet read, but plan to; as well as connections to whole disciplines, fields, and social phenomena. Reading for intertextuality means looking for opportunities to connect texts with each other, and keeping track of those connections in a productive way.

This means note-taking is essential to intertextual reading. Once you have thought carefully about why you are reading a text, what types of information to look for, and what you will do with that information, you can better decide how to keep track of that information. In regards to literature reviews, one type of graphic organizer dominates: the Synthesis Matrix.

The synthesis matrix is a way to keep track of the themes, concepts, and patterns that are emerging from your reading—NOT all the individual content of each article. This is important, yes, and you will need the citations, but literature reviews move one step further into the topic than simply identifying the pieces. You will need to synthesize.

If you have an annotated bibliography of sources already, it is the perfect way to start your synthesis matrix. An annotated bibliography is often the first step in preparing for a literature review, and is quite similar to an ingredient list, if we are using the metaphor from the introduction. (For a detailed description of how to write an annotated bibliography, see Chapter 1 ).

In your annotations, you will have selected the most important information that text supplies in relation to your topic. For an example, let’s take the Conference on College Composition and Communication’s statement “ Students’ Right to Their Own Language ,” which contains two annotated bibliographies. The second uses more recent sources and looks most like the annotated bibliographies you will write as a student, so let’s start there.

Example 3.8: Here are three annotations from that bibliography. As you read, take notice of the different highlighted colors. Phrases italicized and highlighted green identify ideas related to linguistic identity , phrases bolded and highlighted in blue identify concepts related to grammar analysis , and phrases underlined and highlighted orange identify groups and ideas related to educational objectives :

Fought, Carmen. Chicano English in Context. New York: Palgrave Macmillan, 2003.

Based primarily on data collected from adolescent and young adult native speakers in Los Angeles , this book is a comprehensive sociolinguistic study of language and language change in Latino/a communities. It provides the basics of Chicano English (CE) structure (phonology, syntax, and semantics) and its connection to the social and cultural identity of its speakers, along with detailed analyses of particular sociolinguistic variables. Emphasis is given to the historical, social, and linguistic contexts of CE. In addition, the differences between native and non-native CE speakers are covered. A final chapter discusses the future of research on CE.

Lippi-Green, Rosina. English with an Accent: Language, Ideology, and Discrimination in the United States . London and New York: Routledge, 1997.

The author examines linguistic facts about the structure and function of language , explores commonly held myths about language, and develops a model of “the language subordination process.” Then, using a case-study approach, she applies the model to specific institutional practices (e.g., in education, news media, business) to show how false assumptions about language lead to language subordination. The author analyzes specific groups and individuals (speakers of African American English, Southern U.S. English, and the foreign-language accent of Latinos and Asian Americans) and discusses why and how some embrace linguistic assimilation while others resist it.

Nero, Shondel J. Englishes in Contact: Anglophone Caribbean Students in an Urban College. Cresskill, NJ: Hampton Press, 2001.

This qualitative study of four anglophone Caribbean students at a New York City college offers an in-depth examination of the students’ written and spoken language and the challenges faced by both students and teachers as such students acquire academic literacy. Case studies of the four participants include excerpts from tape-recorded interviews, which reflect their linguistic self-perception, and sociolinguistic and educational experiences in their home countries and in New York City. Samples of their college writing over four semesters are represented and analyzed on morphosyntactic and discourse levels to determine the patterns that emerge when Creole English speakers attempt to write Standard Written English. Related issues such as language and identity , language attitudes, and educational responses to ethnolinguistic diversity are also discussed.

Once you have identified a concept like “language and identity” for your literature review, you can start getting “intertextual”! Review your other annotated sources and your new sources for their discussion of language and identity, as well as parallel concepts—what else do researchers address when they discuss language and identity? What do they discuss instead? Go back to the methods you used to come up with key terms for your literature search—the same strategies now apply to your reading. Also look for “umbrella” concepts, patterns in methodologies—anything that emerges while you read intertextually, focusing on the text in front of you while also remembering all the others you read before. Look for the themes in your annotated bibliography and keep track of the page numbers where these themes appear—plan to go back to those pages several times as you write your literature review.

This is a different type of reading than you did for the annotated bibliography, and might mean you go back and reread your sources several times in this new way—don’t think of this as just repeating labor you have already performed. This is new work, designed to uncover new things in the research. Re-reading articles multiple times is something all serious writers do, and something you should do, too. It isn’t redundant, it is recur sive .

Table 3.3: Synthesis Matrix for Individuals’ Choices in Linguistic Identity

Put your sources into conversations around your themes, as shown in the table above. Notice that the top row names the themes covered in that column, put into original wording similar, but not identical, to the wording in the annotated bibliographies. Not every source will address every topic—not every article is the same. The last row starts to describe what is happening in each column across the whole collection of texts. In this way, your synthesis matrix takes the ingredient list provided by the annotated bibliography and makes it into a recipe for your final product—the literature review.

More Resources 3.4: Synthesis Matrix

VI. Writing Strategies: Citation, Quotation, and Paraphrase

Citation is when you use the work of other authors in your writing and mark that portion of your writing so your reader understands what idea is being “borrowed.” Citation also tells your reader where they could find that original idea in the original text, and how your text fits together with the web of other texts related to your topic: in other words, citations help create intertextuality. A citation placed in your sentences should refer directly to the full bibliographic information in your Works Cited or References page.

As you read in Chapter 1, there are different styles of citation including AMA, APA, CMS, and MLA. You can refer back to that chapter for a more detailed explanation of each. In this section, we’ll cover the basics that are common to citation practices. Most academic styles use the original author’s last name as the central part of the in-text citation, since References pages usually list cited works alphabetically by last name, but some use footnotes or endnotes instead, listing works in the order they were cited. It is important to know which academic style you are using for your literature review so that you can make the right choice.

In-text citation takes one of two forms: parenthetical or narrative. In a narrative citation the author of the original work is mentioned in the sentence.

Example 3.9: Here’s an example taken from the introduction of the same literature review discussed in the Research Strategies: Developing a Methodology section of this chapter.

Several pieces offered a comprehensive review of the historical literature on the formation of Black English as a construct in the context of slavery and Jim Crow, and the historical teaching of Black English within the U .S. context, including Wheeler ( 2016 ) and Alim and Baugh (2007). Wheeler (2016) equated Standard English with ‘White’ English and challenged its hegemony in dialectically diverse classrooms. She named the “racism inherent in [fostering] bidialectalism [th rough teaching]” (p. 380), arguing that we are acknowledging that the only way for African-Americans to be upwardly mobile was to learn how to speak ‘White’ English. Alim (2010) , explained, “By uncritically presenting language varieties as ‘equal’ but diff ering in levels of ‘appropriateness,’ language and Dialect Awareness programs run the risk of silently legitimizing ‘Standard English’” (p. 215)…. Current work addressing AAVE studies has been shifting focus to translingualism and to promoting such pedag ogies as code-meshing (Young, Barrett, Young Rivera and Lovejoy, 2014) and translanguaging (García & Wei, García and Wei, 2014) , embedded in a critical analysis of the racial logics underpinning the denigration of some languages. This work, combined with e xtensive examinations of the connections between race, language, teaching, and identity ( e.g. Flores & Rosa, 2015; Alim et al., 2016 ), has laid a foundation for a raciolinguistics approach to teaching, which we return to later in this article. (Von Esch et al., 2020, p. 399, emphasis added .)

In the first sentence, we see two narrative citations just before the period. These citations state the authors’ names as a part of the sentence, and put the publication date of the articles in parenthesis. It makes sense to use a narrative citation in the topic sentence, since most of the paragraph is a synthesis of Wheeler and Alim’s research. The second sentence starts with Wheeler’s name in the subject position, and the fourth sentence starts with Alim’s name in the subject position—both are narrative citations, a form chosen by the author to emphasize the importance and similarities in the two articles.

In the last two sentences, we see parenthetical citations. The citation information is in parenthesis within the sentences, which focuses the reader on the ideas, not the research itself. Imagine you were reading this article out loud—you would most certainly say the narrative citations “Wheeler” and “Alim”; you might choose not to say “Young, Barrett, Young-Rivera, & Lovejoy, 2014,” though, and no one listening to you would notice the omission. This is the most important difference between narrative and parenthetical citation—narrative draws attention to the researchers, while parenthetical allows a focus on ideas. In academic writing, you often have reason to use both, but it is important to note that using parenthetical citation is less disruptive to your voice—it keeps a reader focused on the ideas you are explaining.

Usually you are citing a type of quotation in your text (although different disciplines have other situations that they cite). Direct quotation and paraphrase are usually what we talk about when we talk about using resources in your writing, although summary is cited as well.

Direct quotation is when you take the original words of one author and place them in your own text. When you quote in your own writing, you mark the copied text—usually with quotation marks “” around the text and a citation afterwards. Quoting is useful when the original author is an important authority on a topic or if you want to define/describe another’s point of view in a way that leaves no room for misinterpretation.

In a literature review, a direct quote will almost always be accompanied by a narrative citation. But direct quoting can cause some issues in your own text, such as a sudden shift in voice and a loss of cohesion; the potential for misunderstanding and misrepresentation, since the quote has been separated from its original context; and wordiness —quotes can take up too much space both in terms of the quote itself, and of the explanation and context you must provide for the introduced idea. For these reasons, literature reviews do not contain much direct quoting.

Paraphrasing is a way to accomplish similar goals to direct quoting without causing the same problems. Paraphrasing is when you use only the original author’s key terms and ideas, but your own words. Paraphrasing still contains a citation afterwards that directs the reader to the full bibliographic information in your Works Cited, but does not require quotation marks since the language is yours. Paraphrase may be longer or shorter than the original author’s text, and uses both narrative and parenthetical citation. Paraphrase also allows you to cite more than one piece of research containing the same idea in a single sentence, such as the last sentence in the example paragraph above. This kind of citation string is important to literature reviews because it clearly identifies patterns and trends in research findings.

Key Takeaways

• Literature reviews are a synthesis of what other researchers have discovered on your topic. Think of reviews as “the big picture.”
• Taking so much information from other sources can get confusing–use section headings to keep your review organized and clear.
• Diverse citation, quotation, and paraphrasing techniques are necessary to help your reader understand where the ideas are coming from, AND to help make the ideas “stick together.”
• Keeping all the new knowledge you are learning from your sources organized is hard! Take notes using citations and use a graphic organizer to keep yourself on track.

Fernandez, Lord, H., Halcomb, E., Moxham, L., Middleton, R., Alananzeh, I., & Ellwood, L. (2020). Implications for COVID-19: A systematic review of nurses’ experiences of working in acute care hospital settings during a respiratory pandemic. International Journal of Nursing Studies , 111. https://doi.org/10.1016/j.ijnurstu.2020.103637

Kassin, S. M., & Gudjonsson, G. H. (2004). The psychology of confessions. Psychological Science in the Public Interest , 5 (2), 33–67. https://doi.org/10.1111/j.1529-1006.2004.00016.x

National Council of Teachers of English. (2018, June 16). Students’ right to their own language (with bibliography) . Conference on College Composition and Communication. Retrieved July 24, 2022, from https://cccc.ncte.org/cccc/resources/positions/srtolsummary

NEIU Libraries. (2020). “How should I search in a database?”  YouTube . https://www.youtube.com/watch?v=8fgBF0EuH_o

Ratcliffe, E. (2021). Summary Flowchart [Image]. Frontiers in Psychology. https://www.frontiersin.org/articles/10.3389/fpsyg.2021.570563/full#B3

Ratcliffe, E. (2021). Sound and soundscape in restorative natural environments: A narrative literature review. Frontiers in Psychology , 12 . https://doi.org/10.3389/fpsyg.2021.570563

Sasaki. K. (2022). Synthesis and Recipes [Image].

Von Esch, K., Motha, S., & Kubota, R. (2020). Race and language teaching. Language Teaching, 53 (4), 391-421. doi:10.1017/S0261444820000269

Writing for Inquiry and Research Copyright © 2023 by Charitianne Williams is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License , except where otherwise noted.

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Literature Reviews

• Introduction: What, Who & Why
• Define a topic
• Identify keywords

Identifying keywords

Comprehesive vs precise, using text mining to identify keywords.

• More search tips
• Understand & Analyse
• More resources
• Accessing help
• Systematic Style Reviews Guide

It is important to find all the relevant keywords for the topic to ensure the search is comprehensive by identifying:

• different spellings, tenses and word variants of keywords
• related concepts
• names of people or authors associated with these ideas

There are many  ways to locate these terms, including

• recommended readings, textbooks and other review articles that provide an overview of the field of  research
• dictionaries, thesauri, handbooks and encyclopedias that provide definitions and general information about topics.
• database thesauri or subject headings that tell you which terms are used in the databases and professional literature.
• text mining tools that allow you to analyse large amounts of text or information and identify commonly used terms in the field.

The process of searching will also help identify more terms that you should be adding to your list.

There needs to be a balance in searching between making the search comprehensive enough to encompass everything on the topic and precise enough to only capture those results that are specifically relevant.

Both approaches have advantages and disadvantages

Increasing the comprehensiveness (or sensitivity) of a search will reduce its precision and will retrieve more non-relevant articles.

Text mining will help identify how often terms come up in the literature and help identify other related terms and subject headings that have not been considered or thought of as being useful.

Text mining is a process used to look at large amounts of text and find relationships in the results by using computer programs designed to extract and analyse this data. 

It is used to categorise information and identify trends and patterns which can be done across large documents or multiple sources (or both).

1. Mining for terms Use these tools to find alternate search terms that are related by identifying how often keywords appear and which other terms appear with them by number of occurrences.

2. Mine within the text Locate terms within blocks of text (e.g. an article) to find word patterns and frequency. More frequent words are more likely to be relevant to the topic.

3. Use visualising tools These tools create word clouds related to search terms

These are just some of the tools available for mining text that are available on the web. There is also both commercial and free software that can be downloaded and installed. The web pages linked below have lists of yet more tools.

Further reading:

• EPC Methods: An Exploration of the Use of Text-Mining Software in Systematic Reviews Paynter R., Bañez L. L., Berliner E., Erinoff, E., Lege-Matsuura, J., Potter, S., & Uhl, S. (2016). EPC methods: An exploration of the use of text-mining software in systematic reviews. Retrieved from: https://www.ncbi.nlm.nih.gov/books/NBK362044/
• << Previous: Search the literature
• Next: More search tips >>
• Last Updated: Aug 28, 2024 3:06 PM
• URL: https://libguides.jcu.edu.au/litreview

Research Methods

• Getting Started
• Literature Review Research
• Research Design
• Research Design By Discipline
• SAGE Research Methods
• Teaching with SAGE Research Methods

Literature Review

• What is a Literature Review?
• What is NOT a Literature Review?
• Purposes of a Literature Review
• Types of Literature Reviews
• Literature Reviews vs. Systematic Reviews
• Systematic vs. Meta-Analysis

Literature Review  is a comprehensive survey of the works published in a particular field of study or line of research, usually over a specific period of time, in the form of an in-depth, critical bibliographic essay or annotated list in which attention is drawn to the most significant works.

Also, we can define a literature review as the collected body of scholarly works related to a topic:

• Summarizes and analyzes previous research relevant to a topic
• Includes scholarly books and articles published in academic journals
• Can be an specific scholarly paper or a section in a research paper

The objective of a Literature Review is to find previous published scholarly works relevant to an specific topic

• Help gather ideas or information
• Keep up to date in current trends and findings
• Help develop new questions

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Helps focus your own research questions or problems
• Discovers relationships between research studies/ideas.
• Suggests unexplored ideas or populations
• Identifies major themes, concepts, and researchers on a topic.
• Tests assumptions; may help counter preconceived ideas and remove unconscious bias.
• Identifies critical gaps, points of disagreement, or potentially flawed methodology or theoretical approaches.
• Indicates potential directions for future research.

All content in this section is from Literature Review Research from Old Dominion University 

Keep in mind the following, a literature review is NOT:

Not an essay 

Not an annotated bibliography  in which you summarize each article that you have reviewed.  A literature review goes beyond basic summarizing to focus on the critical analysis of the reviewed works and their relationship to your research question.

Not a research paper   where you select resources to support one side of an issue versus another.  A lit review should explain and consider all sides of an argument in order to avoid bias, and areas of agreement and disagreement should be highlighted.

A literature review serves several purposes. For example, it

• provides thorough knowledge of previous studies; introduces seminal works.
• helps focus one’s own research topic.
• identifies a conceptual framework for one’s own research questions or problems; indicates potential directions for future research.
• suggests previously unused or underused methodologies, designs, quantitative and qualitative strategies.
• identifies gaps in previous studies; identifies flawed methodologies and/or theoretical approaches; avoids replication of mistakes.
• helps the researcher avoid repetition of earlier research.
• suggests unexplored populations.
• determines whether past studies agree or disagree; identifies controversy in the literature.
• tests assumptions; may help counter preconceived ideas and remove unconscious bias.

As Kennedy (2007) notes*, it is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the original studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally that become part of the lore of field. In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews.

Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are several approaches to how they can be done, depending upon the type of analysis underpinning your study. Listed below are definitions of types of literature reviews:

Argumentative Review      This form examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to to make summary claims of the sort found in systematic reviews.

Integrative Review      Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review      Few things rest in isolation from historical precedent. Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review      A review does not always focus on what someone said [content], but how they said it [method of analysis]. This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection and data analysis, and helps highlight many ethical issues which we should be aware of and consider as we go through our study.

Systematic Review      This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyse data from the studies that are included in the review. Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?"

Theoretical Review      The purpose of this form is to concretely examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review help establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

* Kennedy, Mary M. "Defining a Literature."  Educational Researcher  36 (April 2007): 139-147.

All content in this section is from The Literature Review created by Dr. Robert Larabee USC

Robinson, P. and Lowe, J. (2015),  Literature reviews vs systematic reviews.  Australian and New Zealand Journal of Public Health, 39: 103-103. doi: 10.1111/1753-6405.12393

What's in the name? The difference between a Systematic Review and a Literature Review, and why it matters . By Lynn Kysh from University of Southern California

Systematic review or meta-analysis?

A  systematic review  answers a defined research question by collecting and summarizing all empirical evidence that fits pre-specified eligibility criteria.

A  meta-analysis  is the use of statistical methods to summarize the results of these studies.

Systematic reviews, just like other research articles, can be of varying quality. They are a significant piece of work (the Centre for Reviews and Dissemination at York estimates that a team will take 9-24 months), and to be useful to other researchers and practitioners they should have:

• clearly stated objectives with pre-defined eligibility criteria for studies
• explicit, reproducible methodology
• a systematic search that attempts to identify all studies
• assessment of the validity of the findings of the included studies (e.g. risk of bias)
• systematic presentation, and synthesis, of the characteristics and findings of the included studies

Not all systematic reviews contain meta-analysis. 

Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review.  More information on meta-analyses can be found in  Cochrane Handbook, Chapter 9 .

A meta-analysis goes beyond critique and integration and conducts secondary statistical analysis on the outcomes of similar studies.  It is a systematic review that uses quantitative methods to synthesize and summarize the results.

An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings.  Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted.  In that case, an integrative review is an appropriate strategy. 

Some of the content in this section is from Systematic reviews and meta-analyses: step by step guide created by Kate McAllister.

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Ten Simple Rules for Writing a Literature Review

Marco pautasso.

1 Centre for Functional and Evolutionary Ecology (CEFE), CNRS, Montpellier, France

2 Centre for Biodiversity Synthesis and Analysis (CESAB), FRB, Aix-en-Provence, France

Literature reviews are in great demand in most scientific fields. Their need stems from the ever-increasing output of scientific publications [1] . For example, compared to 1991, in 2008 three, eight, and forty times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [2] . Given such mountains of papers, scientists cannot be expected to examine in detail every single new paper relevant to their interests [3] . Thus, it is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews can lead to new synthetic insights and are often widely read [4] . For such summaries to be useful, however, they need to be compiled in a professional way [5] .

When starting from scratch, reviewing the literature can require a titanic amount of work. That is why researchers who have spent their career working on a certain research issue are in a perfect position to review that literature. Some graduate schools are now offering courses in reviewing the literature, given that most research students start their project by producing an overview of what has already been done on their research issue [6] . However, it is likely that most scientists have not thought in detail about how to approach and carry out a literature review.

Reviewing the literature requires the ability to juggle multiple tasks, from finding and evaluating relevant material to synthesising information from various sources, from critical thinking to paraphrasing, evaluating, and citation skills [7] . In this contribution, I share ten simple rules I learned working on about 25 literature reviews as a PhD and postdoctoral student. Ideas and insights also come from discussions with coauthors and colleagues, as well as feedback from reviewers and editors.

Rule 1: Define a Topic and Audience

How to choose which topic to review? There are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature just pondering what to review. On the one hand, if you take several years to choose, several other people may have had the same idea in the meantime. On the other hand, only a well-considered topic is likely to lead to a brilliant literature review [8] . The topic must at least be:

• interesting to you (ideally, you should have come across a series of recent papers related to your line of work that call for a critical summary),
• an important aspect of the field (so that many readers will be interested in the review and there will be enough material to write it), and
• a well-defined issue (otherwise you could potentially include thousands of publications, which would make the review unhelpful).

Ideas for potential reviews may come from papers providing lists of key research questions to be answered [9] , but also from serendipitous moments during desultory reading and discussions. In addition to choosing your topic, you should also select a target audience. In many cases, the topic (e.g., web services in computational biology) will automatically define an audience (e.g., computational biologists), but that same topic may also be of interest to neighbouring fields (e.g., computer science, biology, etc.).

Rule 2: Search and Re-search the Literature

After having chosen your topic and audience, start by checking the literature and downloading relevant papers. Five pieces of advice here:

• keep track of the search items you use (so that your search can be replicated [10] ),
• keep a list of papers whose pdfs you cannot access immediately (so as to retrieve them later with alternative strategies),
• use a paper management system (e.g., Mendeley, Papers, Qiqqa, Sente),
• define early in the process some criteria for exclusion of irrelevant papers (these criteria can then be described in the review to help define its scope), and
• do not just look for research papers in the area you wish to review, but also seek previous reviews.

The chances are high that someone will already have published a literature review ( Figure 1 ), if not exactly on the issue you are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your issue, my advice is not to give up, but to carry on with your own literature review,

The bottom-right situation (many literature reviews but few research papers) is not just a theoretical situation; it applies, for example, to the study of the impacts of climate change on plant diseases, where there appear to be more literature reviews than research studies [33] .

• discussing in your review the approaches, limitations, and conclusions of past reviews,
• trying to find a new angle that has not been covered adequately in the previous reviews, and
• incorporating new material that has inevitably accumulated since their appearance.

When searching the literature for pertinent papers and reviews, the usual rules apply:

• be thorough,
• use different keywords and database sources (e.g., DBLP, Google Scholar, ISI Proceedings, JSTOR Search, Medline, Scopus, Web of Science), and
• look at who has cited past relevant papers and book chapters.

Rule 3: Take Notes While Reading

If you read the papers first, and only afterwards start writing the review, you will need a very good memory to remember who wrote what, and what your impressions and associations were while reading each single paper. My advice is, while reading, to start writing down interesting pieces of information, insights about how to organize the review, and thoughts on what to write. This way, by the time you have read the literature you selected, you will already have a rough draft of the review.

Of course, this draft will still need much rewriting, restructuring, and rethinking to obtain a text with a coherent argument [11] , but you will have avoided the danger posed by staring at a blank document. Be careful when taking notes to use quotation marks if you are provisionally copying verbatim from the literature. It is advisable then to reformulate such quotes with your own words in the final draft. It is important to be careful in noting the references already at this stage, so as to avoid misattributions. Using referencing software from the very beginning of your endeavour will save you time.

Rule 4: Choose the Type of Review You Wish to Write

After having taken notes while reading the literature, you will have a rough idea of the amount of material available for the review. This is probably a good time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather short reviews focusing on the last few years, with a limit on the number of words and citations. A mini-review is not necessarily a minor review: it may well attract more attention from busy readers, although it will inevitably simplify some issues and leave out some relevant material due to space limitations. A full review will have the advantage of more freedom to cover in detail the complexities of a particular scientific development, but may then be left in the pile of the very important papers “to be read” by readers with little time to spare for major monographs.

There is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and interpretation of each reviewed study, integrative reviews attempt to find common ideas and concepts from the reviewed material [12] . A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews attempt to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [13] , [14] . When systematic reviews analyse quantitative results in a quantitative way, they become meta-analyses. The choice between different review types will have to be made on a case-by-case basis, depending not just on the nature of the material found and the preferences of the target journal(s), but also on the time available to write the review and the number of coauthors [15] .

Rule 5: Keep the Review Focused, but Make It of Broad Interest

Whether your plan is to write a mini- or a full review, it is good advice to keep it focused 16 , 17 . Including material just for the sake of it can easily lead to reviews that are trying to do too many things at once. The need to keep a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap between fields [18] . If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may be inclined to include material from both parent fields, epidemiology and the study of cultural diffusion. This may be necessary to some extent, but in this case a focused review would only deal in detail with those studies at the interface between epidemiology and the spread of ideas.

While focus is an important feature of a successful review, this requirement has to be balanced with the need to make the review relevant to a broad audience. This square may be circled by discussing the wider implications of the reviewed topic for other disciplines.

Rule 6: Be Critical and Consistent

Reviewing the literature is not stamp collecting. A good review does not just summarize the literature, but discusses it critically, identifies methodological problems, and points out research gaps [19] . After having read a review of the literature, a reader should have a rough idea of:

• the major achievements in the reviewed field,
• the main areas of debate, and
• the outstanding research questions.

It is challenging to achieve a successful review on all these fronts. A solution can be to involve a set of complementary coauthors: some people are excellent at mapping what has been achieved, some others are very good at identifying dark clouds on the horizon, and some have instead a knack at predicting where solutions are going to come from. If your journal club has exactly this sort of team, then you should definitely write a review of the literature! In addition to critical thinking, a literature review needs consistency, for example in the choice of passive vs. active voice and present vs. past tense.

Rule 7: Find a Logical Structure

Like a well-baked cake, a good review has a number of telling features: it is worth the reader's time, timely, systematic, well written, focused, and critical. It also needs a good structure. With reviews, the usual subdivision of research papers into introduction, methods, results, and discussion does not work or is rarely used. However, a general introduction of the context and, toward the end, a recapitulation of the main points covered and take-home messages make sense also in the case of reviews. For systematic reviews, there is a trend towards including information about how the literature was searched (database, keywords, time limits) [20] .

How can you organize the flow of the main body of the review so that the reader will be drawn into and guided through it? It is generally helpful to draw a conceptual scheme of the review, e.g., with mind-mapping techniques. Such diagrams can help recognize a logical way to order and link the various sections of a review [21] . This is the case not just at the writing stage, but also for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can be very helpful to structure the text too [22] .

Rule 8: Make Use of Feedback

Reviews of the literature are normally peer-reviewed in the same way as research papers, and rightly so [23] . As a rule, incorporating feedback from reviewers greatly helps improve a review draft. Having read the review with a fresh mind, reviewers may spot inaccuracies, inconsistencies, and ambiguities that had not been noticed by the writers due to rereading the typescript too many times. It is however advisable to reread the draft one more time before submission, as a last-minute correction of typos, leaps, and muddled sentences may enable the reviewers to focus on providing advice on the content rather than the form.

Feedback is vital to writing a good review, and should be sought from a variety of colleagues, so as to obtain a diversity of views on the draft. This may lead in some cases to conflicting views on the merits of the paper, and on how to improve it, but such a situation is better than the absence of feedback. A diversity of feedback perspectives on a literature review can help identify where the consensus view stands in the landscape of the current scientific understanding of an issue [24] .

Rule 9: Include Your Own Relevant Research, but Be Objective

In many cases, reviewers of the literature will have published studies relevant to the review they are writing. This could create a conflict of interest: how can reviewers report objectively on their own work [25] ? Some scientists may be overly enthusiastic about what they have published, and thus risk giving too much importance to their own findings in the review. However, bias could also occur in the other direction: some scientists may be unduly dismissive of their own achievements, so that they will tend to downplay their contribution (if any) to a field when reviewing it.

In general, a review of the literature should neither be a public relations brochure nor an exercise in competitive self-denial. If a reviewer is up to the job of producing a well-organized and methodical review, which flows well and provides a service to the readership, then it should be possible to be objective in reviewing one's own relevant findings. In reviews written by multiple authors, this may be achieved by assigning the review of the results of a coauthor to different coauthors.

Rule 10: Be Up-to-Date, but Do Not Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need awareness not just of the overall direction and achievements of a field of inquiry, but also of the latest studies, so as not to become out-of-date before they have been published. Ideally, a literature review should not identify as a major research gap an issue that has just been addressed in a series of papers in press (the same applies, of course, to older, overlooked studies (“sleeping beauties” [26] )). This implies that literature reviewers would do well to keep an eye on electronic lists of papers in press, given that it can take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain point in time, but given that peer review can be a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is particularly challenging, because there is little perspective with which to gauge their significance and impact on further research and society.

Inevitably, new papers on the reviewed topic (including independently written literature reviews) will appear from all quarters after the review has been published, so that there may soon be the need for an updated review. But this is the nature of science [27] – [32] . I wish everybody good luck with writing a review of the literature.

Acknowledgments

Many thanks to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, M. Garbelotto, O. Holdenrieder, M. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous draft.

Funding Statement

This work was funded by the French Foundation for Research on Biodiversity (FRB) through its Centre for Synthesis and Analysis of Biodiversity data (CESAB), as part of the NETSEED research project. The funders had no role in the preparation of the manuscript.

How to Write a Literature Review

Learn what a literature review is, where it is used, and the structure it should follow, including how to refer to studies and establish themes. We provides tips on writing a literature review, such as stating your research question, selecting key terms, and finding relevant literature on your topic.

Updated on May 17, 2023

A literature review is an overview of the existing literature on a particular topic. It provides a concise summary and critical analysis of existing publications. This justifies why the study was conducted. It also helps the reader understand the topic and see areas for future research. It can be part of a manuscript’s introduction section or a required part of an academic thesis. It can also be a standalone paper, such as a narrative review.

This article discusses what a literature review is when it’s part of a research paper. It provides strategies, tools, and tips for writing a good review.

What is a literature review, and where is it used?

A literature review is an organized summary of existing literature on a topic or research question. It’s used to help readers understand what has been done before related to the topic you’re writing on.

It shows how your study fits into the literature, why your study is needed, and what novel insights your study will bring to the literature.

In that sense, a literature review justifies your work and its potential impact. Literature reviews are also valuable for other researchers, as they can overview a specific topic.

A literature review is used in academic documents, including manuscripts, theses and dissertations, and in standalone papers such as systematic reviews and narrative reviews.

In a manuscript or dissertation, the literature review is presented as background information in the introduction section. Here, it summarizes prior research on the key concepts the paper focuses on, identifies gaps in the literature, and provides context for why the current study is needed. It focuses on summarizing articles that provide specific evidence relating to the topic of the larger manuscript and is very narrowly focused.

In contrast, a standalone literature review is a comprehensive and critical analysis of the existing research and literature on a specific topic. It synthesizes the current state of knowledge on the topic, identifies gaps, contradictions, and future directions for research. A literature review paper is typically longer, more comprehensive, and applies a study methodology.

What structure do literature reviews follow?

Literature reviews follow a logical structure, meaning every sentence logically leads to the next. They begin with a broad overview of the topic and then narrow down to specific research carried out on that topic in a way that builds on the previous information. Supporting studies are discussed one-by-one or they’re grouped by themes. They may or may not specifically indicate the authors by name. That depends on personal style and guidelines.

Referring to studies

For example, the literature review in Howden et al. (2018), reporting on a randomized controlled trial (RCT) on fitness and heart failure, first states the overall theme: sedentary aging’s association with worsening cardiovascular health. In concise sentences, it then lists the themes along with subscript numbers of the supporting literature, e.g., “...middle age is the strongest predictor of future heart failure.5–7”. No authors are named. This may be because of the referencing style (using numbers leading to the References list, unlike, for instance, APA, which uses last names), or it may be the authors’ preference.

Tramontano et al. (2021), on remote work , lists authors’ names along with the supporting research. In some cases, the names are in parentheses (per APA style) and in other cases, (e.g., ...Gonzales Vazquez and colleagues (2019) indicated...) the names represent the study. Again, it’s a combination of referencing style and authors’ preference.

Establish themes

As the literature review progresses, you synthesize the information from the articles. Articles are grouped together by theme or evidence (i.e., supporting or contrasting), with relevant citations giving support. Typically, findings are condensed and summarized concisely (i.e., in one or a couple of sentences).

For example, if you were exploring how processed food affects heart health, articles in the literature review might be grouped into categories such as heart health in general, processed foods, and the negative effects of processed foods on general heart health. You’d then summarize the key findings for each category with relevant citations.

As such, a literature review in a manuscript is not simply a chronological list of articles and their findings. Rather, it’s a report and analysis of the existing literature. It weaves a narrative that underpins your own study.

Writing your literature review

State your research question .

The first step to writing a good literature review is stating your research question.

If you’re writing a manuscript or dissertation, you likely already know what your research question is. Be sure it’s clearly presented at the end of the introductory paragraph so the reader immediately knows what the study will be about.

Select key terms

Next, identify several key words/terms/phrases that will be used to query your search for relevant literature.

For example, if your manuscript is about the effects of processed foods on heart health, you will want to use keywords such as “cardiovascular,” “processed foods,” and “heart disease” to retrieve relevant publications.

Find relevant literature on your topic

Most researchers have a specialty or a few specialties. Reading other studies should already be part of your day-to-day practice. So it’s very unusual to start a literature review from zero. You probably already have a folder full of PDFs (or, ideally, a reference manager full of well-organized articles in digital format).

For your current research, you’ll then add further literature in more specific and specialized areas. You’ll need to update your personal library. And you may find you lack sufficient publications in a certain area of research. Your literature review will address all these issues. Methods for diving in include databases, review articles, and asking colleagues and other researchers.

Online databases

Searching with databases often requires a combination of free and paid sources.

Google Scholar is probably the most commonly known search engine for academic literature because, well, it’s Google. Type titles, keywords, authors, or other entries to find papers on your topic of interest. You don’t need to create an account, but just because a publication is listed in Scholar doesn’t mean you can access the full text. Still, its powerful search features can help you rapidly narrow your search. You can then find publications in a database for which you have a subscription.

EBSCO and ProQuest are commonly available in universities’ online libraries, and databases like PubMed are comprehensive scientific collections. Some databases are open access, while others require a subscription to fully access the articles. Hopefully, you have access through your university or institution.

There are also publisher-managed search engines and databases like ScienceDirect or Scopus , as well as Wiley Online Library . These usually require a subscription.

Elicit is an AI-based search engine. Ask a research question and find relevant literature. It also suggests questions based on your input for better results. No account is needed.

Zendy is a search engine dedicated to open access journals. It’s accessible once you create an account.

Colleagues, fellow researchers

Asking your colleagues or fellow researchers in your field can be a great resource for finding additional studies. You can also look for highly cited papers in your field or search for articles from known experts in your field.

Other literature reviews, review articles, and reference lists

Previous review papers on your topic, introduction sections of articles (which contain their own literature reviews), are reference lists of papers are all great tools for finding additional articles. Look through the reference lists of previous prior review papers to locate other relevant articles.

With this approach, you’ll find yourself diving down one rabbit hole after another. And it can get overwhelming, so scan quickly, keep notes, and use a good reference manager (see below). After a while, you’ll start to see the same publications emerge. You’ll start to recognize the seminal pieces as well as highly specific studies on limited populations.

Software and reference managers

Apps like Connected Papers can help expand your collection and ensure you’re not missing any articles. With this tool, you can search for a work and then see it visualized through other articles it references, and that referenced it. It’s shown as a network of connected papers – fantastic for visual types.

Reference managers like EndNote and Mendeley are helpful tools for organizing your papers and adding citations to your manuscript. You can download them to your computer and easily search for the information you’ve read before, saving a lot of time in the writing process. While they both require creating an account, Mendeley is free. Paperpile is an excellent lighter-weight option.

Organize your sources

When you’ve compiled sufficient publications via your literature search, extract relevant information for your research question.

Identify themes

First, identify the most relevant papers for your research question. One good approach is to read the abstract and methods sections to understand the main findings.

Narrow down your list to articles that have a research question as similar as possible to yours. Then, group them by themes or evidence. For instance, group articles showing that processed foods lead to increased rates of heart disease in one section.

Include contradictory evidence to fully cover the scope of the topic. This will help you better organize the sections for your review later.

Define your key concepts

Every good review section begins with specific definitions of the concepts the paper will focus on. They should be defined in the abstract and introduction.

Write an outline

Write an outline with subheadings representing categories or themes your review will cover. Under each theme, enter a few references or key points that reflect what you want to convey to your reader in that section.

Organize the subheadings logically so that one idea flows into the next. Don’t jump back and forth between concepts. For example, if you’re establishing a common, evidence-supported definition of heart disease, focus only on that. Bringing in other diseases will confuse the reader. If you need to compare with other diseases, that’s probably cause for another subsection.

Review previous articles on your topic and check how the authors structured their introduction section to get ideas for your outline.

For longer reviews, you can use tables to present the literature and key themes more clearly for the reader. Tables are especially useful in dedicated review papers like narrative reviews.

Write your literature review

Following your outline, expand on your notes with sentences and paragraphs, including relevant citations (see the section above for examples of how these are typically written). Use clear and concise language. Make sure all your paragraphs have a dedicated topic sentence that reflects what the rest of the paragraph is about.

Start your review broadly, then use your prior research to narrow down to why your research question is needed. For example, define what heart disease is broadly, then narrow down to how specific processed foods can impact it and what still needs to be investigated (i.e., with your study).

Review your work

After finishing your first draft, revise and refine your work. Here are some key steps.

Refine your literature review

As you write, you may need to expand sections or include more evidence. Read over your review several times and determine if it’s conveying the information you want to get across clearly and adjust accordingly.

Omit unnecessary information

In scientific communication, less is more, so avoid making your review too long. Remove unnecessary information and avoid being too wordy. As a general rule, aim for just one idea per sentence and no more than around 15–20 words per sentence.

A credible citation (or citations) should support every assertion. But it can also get tempting to follow irrelevant paths that aren’t immediately relevant to the study you’re doing now.

Professional editing can also help you refine wordiness.

Check the logical structure

Check that each section in your review relates to the main research question. Check that every paragraph transitions smoothly to the next and that the ideas flow logically from one argument to the next. Ask yourself, “Does this idea directly relate to my next idea?” (and vice versa).

Also, check for consistency and completeness. Be sure you used the same wording for key concepts throughout your review and that you included all relevant evidence for your arguments.

Check for and remove/correct plagiarism

There are many ways to plagiarize , and some authors don’t even know when they’re doing it. It can be a critical mistake.

Journals use tools such as i Thenticate to detect plagiarism. And being caught plagiarizing can be a cause for a rapid rejection . Avoid plagiarizing by ensuring you cite the original source and don’t copy/paste text unless you use quotation marks. You can check for plagiarism using apps like Grammarly or Trinka , which can also help you improve your writing style and correct grammar mistakes.

Get outside perspectives

Ask a senior researcher or colleague to read your work and provide feedback or criticism. Ask junior researchers as well. Put your ego on the line for the good of rigorous science. Often, those with less experience may be able to see the more basic gaps in logic and clarity, as they bring a less honed and specialized perspective.

Check that you’ve included all references in the format required by the journal (e.g., APA, Vancouver, AMA). Use tools like Mendeley and EndNote to automatically generate a bibliography section based on the references you enter in your document. But do double-check what the software generates. It may be relying on incorrect metadata.

Good example of a literature review in a published article

Good literature reviews should be clear, concise, and informative. They should present enough information on the topic that you can understand the importance of the topic, the relevance of the literature included for the broader field, and what’s still missing from the literature (i.e., where further research is needed).

Here’s a good example:

Heart issues, sedentary lifestyle, exercise (from Howden et al. 2018)

Readable and well-structured, this review quickly highlights the negative relationship between a sedentary lifestyle and heart issues. It concisely reviews previous literature showing the relationship between exercise and heart health, so the reader understands why the study is needed.

Bonus: What’s the difference between a literature review and an annotated bibliography?

An annotated bibliography is a list of references with a brief summary of the results of that reference. It can also include your personal notes on the study and why it’s relevant to your study.

Especially for students, a literature review can be confused with an annotated bibliography. Both these devices detail existing studies. However, they perform quite different functions.

Annotated bibliographies are powerful when you’re writing a dissertation or any longer research piece, as they help you keep track of everything you’ve read and why it’s relevant. You may not publish it, but you can definitely use it when you write your literature review.

So, the key differences between an annotated bibliography are:

• An annotated bibliography is a list of references with no connection established among them, while a literature review is a narrative of all the studies.
• Annotated bibliographies are organized alphabetically by reference, whereas literature reviews are organized by themes or supporting or contrasting evidence. 
• Annotated bibliographies summarize (in a few sentences) each reference, while literature reviews place the publication in context along with other publications.

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Literature Reviews

• What is a Literature Review?
• Steps for Creating a Literature Review
• Providing Evidence / Critical Analysis
• Challenges when writing a Literature Review
• Systematic Literature Reviews

Developing a Literature Review

1. Purpose and Scope

To help you develop a literature review, gather information on existing research, sub-topics, relevant research, and overlaps. Note initial thoughts on the topic - a mind map or list might be helpful - and avoid unfocused reading, collecting irrelevant content.  A literature review serves to place your research within the context of existing knowledge. It demonstrates your understanding of the field and identifies gaps that your research aims to fill. This helps in justifying the relevance and necessity of your study.

To avoid over-reading, set a target word count for each section and limit reading time. Plan backwards from the deadline and move on to other parts of the investigation. Read major texts and explore up-to-date research. Check reference lists and citation indexes for common standard texts. Be guided by research questions and refocus on your topic when needed. Stop reading if you find similar viewpoints or if you're going off topic.

You can use a "Synthesis Matrix" to keep track of your reading notes. This concept map helps you to provide a summary of the literature and its connections is produced as a result of this study. Utilizing referencing software like RefWorks to obtain citations, you can construct the framework for composing your literature evaluation.

2. Source Selection

Focus on searching for academically authoritative texts such as academic books, journals, research reports, and government publications. These sources are critical for ensuring the credibility and reliability of your review. 

• Academic Books: Provide comprehensive coverage of a topic.
• Journal Articles: Offer the most up-to-date research and are essential for a literature review.
• Research Reports: Detailed accounts of specific research projects.
• Government Publications: Official documents that provide reliable data and insights.

3. Thematic Analysis

Instead of merely summarizing sources, identify and discuss key themes that emerge from the literature. This involves interpreting and evaluating how different authors have tackled similar issues and how their findings relate to your research.

4. Critical Evaluation

Adopt a critical attitude towards the sources you review. Scrutinize, question, and dissect the material to ensure that your review is not just descriptive but analytical. This helps in highlighting the significance of various sources and their relevance to your research.

Each work's critical assessment should take into account:

Provenance:  What qualifications does the author have? Are the author's claims backed up by proof, such as first-hand accounts from history, case studies, stories, statistics, and current scientific discoveries? Methodology:  Were the strategies employed to locate, collect, and evaluate the data suitable for tackling the study question? Was the sample size suitable? Were the findings properly reported and interpreted? Objectivity : Is the author's viewpoint impartial or biased? Does the author's thesis get supported by evidence that refutes it, or does it ignore certain important facts? Persuasiveness:  Which of the author's arguments is the strongest or weakest in terms of persuasiveness? Value:  Are the author's claims and deductions believable? Does the study ultimately advance our understanding of the issue in any meaningful way?

5. Categorization

Organize your literature review by grouping sources into categories based on themes, relevance to research questions, theoretical paradigms, or chronology. This helps in presenting your findings in a structured manner.

6. Source Validity

Ensure that the sources you include are valid and reliable. Classic texts may retain their authority over time, but for fields that evolve rapidly, prioritize the most recent research. Always check the credibility of the authors and the impact of their work in the field.

7. Synthesis and Findings

Synthesize the information from various sources to draw conclusions about the current state of knowledge. Identify trends, controversies, and gaps in the literature. Relate your findings to your research questions and suggest future directions for research.

Practical Tips

• Use a variety of sources, including online databases, university libraries, and reference lists from relevant articles. This ensures a comprehensive coverage of the literature.
• Avoid listing sources without analysis. Use tables, bulk citations, and footnotes to manage references efficiently and make your review more readable.
• Writing a literature review is an ongoing process. Start writing early and revise as you read more. This iterative process helps in refining your arguments and identifying additional sources as needed.  

Brown University Library (2024) Organizing and Creating Information. Available at: https://libguides.brown.edu/organize/litreview (Accessed: 30 July 2024).

Pacheco-Vega, R. (2016) Synthesizing different bodies of work in your literature review: The Conceptual Synthesis Excel Dump (CSED) technique . Available at: http://www.raulpacheco.org/2016/06/synthesizing-different-bodies-of-work-in-your-literature-review-the-conceptual-synthesis-excel-dump-technique/ (Accessed: 30 July 2024).

Study Advice at the University of Reading (2024) Literature reviews . Available at: https://libguides.reading.ac.uk/literaturereview/developing (Accessed: 31 July 2024).

Further Reading

Frameworks for creating answerable (re)search questions  How to Guide

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Literature Review

How to search effectively.

• Find examples of literature reviews
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The  Literature searching interactive tutorial  includes self-paced, guided activities to assist you in developing  effective search skills..

1. Identify search words

Analyse your research topic or question.

• What are the main ideas?
• What concepts or theories have you already covered?
• Write down your main ideas, synonyms, related words and phrases.
• If you're looking for specific types of research, use these suggested terms: qualitative, quantitative, methodology, review, survey, test, trend (and more).
• Be aware of UK and US spelling variations. E.g. organisation OR organization, ageing OR aging.
• Interactive Keyword Builder
• Identifying effective keywords

2. Connect your search words

Find results with one or more search words.

Use OR between words that mean the same thing.

E.g.  adolescent  OR  teenager

This search will find results with either (or both) of the search words.

Find results with two search words

Use AND between words which represent the main ideas in the question.

E.g. adolescent AND “physical activity”

This will find results with both of the search words.

Exclude search words

Use NOT to exclude words that you don’t want in your search results.

E.g. (adolescent OR teenager) NOT “young adult”

3. Use search tricks

Search for different word endings.

Truncation *

The asterisk symbol * will help you search for different word endings.

E.g. teen* will find results with the words: teen, teens, teenager, teenagers

Specific truncation symbols will vary. Check the 'Help' section of the database you are searching.

Search for common phrases

Phrase searching “...........”

Double quotation marks help you search for common phrases and make your results more relevant.

E.g. “physical activity” will find results with the words physical activity together as a phrase.

Search for spelling variations within related terms

Wildcards ?

Wildcard symbols allow you to search for spelling variations within the same or related terms.

E.g. wom?n will find results with women OR woman

Specific wild card symbols will vary. Check the 'Help' section of the database you are searching.

Search terms within specific ranges of each other

Proximity  w/#

Proximity searching allows you to specify where your search terms will appear in relation to each other.

E.g.  pain w/10 morphine will search for pain within ten words of morphine

Specific proximity symbols will vary. Check the 'Help' section of the database you are searching.

4. Improve your search results

All library databases are different and you can't always search and refine in the same way. Try to be consistent when transferring your search in the library databases you have chosen.

Narrow and refine your search results by:

• year of publication or date range (for recent or historical research)
• document or source type (e.g. article, review or book)
• subject or keyword (for relevance). Try repeating your search using the 'subject' headings or 'keywords' field to focus your search
• searching in particular fields, i.e. citation and abstract. Explore the available dropdown menus to change the fields to be searched.

When searching, remember to:

Adapt your search and keep trying.

Searching for information is a process and you won't always get it right the first time. Improve your results by changing your search and trying again until you're happy with what you have found.

Keep track of your searches

Keeping track of searches saves time as you can rerun them, store references, and set up regular alerts for new research relevant to your topic.

Most library databases allow you to register with a personal account. Look for a 'log in', 'sign in' or 'register' button to get started.

• Literature review search tracker (Excel spreadsheet)

Manage your references

There are free and subscription reference management programs available on the web or to download on your computer.

• EndNote - The University has a license for EndNote. It is available for all students and staff, although is recommended for postgraduates and academic staff.
• Zotero - Free software recommended for undergraduate students.
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Home » Literature Review – Types Writing Guide and Examples

Literature Review – Types Writing Guide and Examples

Table of Contents

Literature Review

Definition:

A literature review is a comprehensive and critical analysis of the existing literature on a particular topic or research question. It involves identifying, evaluating, and synthesizing relevant literature, including scholarly articles, books, and other sources, to provide a summary and critical assessment of what is known about the topic.

Types of Literature Review

Types of Literature Review are as follows:

• Narrative literature review : This type of review involves a comprehensive summary and critical analysis of the available literature on a particular topic or research question. It is often used as an introductory section of a research paper.
• Systematic literature review: This is a rigorous and structured review that follows a pre-defined protocol to identify, evaluate, and synthesize all relevant studies on a specific research question. It is often used in evidence-based practice and systematic reviews.
• Meta-analysis: This is a quantitative review that uses statistical methods to combine data from multiple studies to derive a summary effect size. It provides a more precise estimate of the overall effect than any individual study.
• Scoping review: This is a preliminary review that aims to map the existing literature on a broad topic area to identify research gaps and areas for further investigation.
• Critical literature review : This type of review evaluates the strengths and weaknesses of the existing literature on a particular topic or research question. It aims to provide a critical analysis of the literature and identify areas where further research is needed.
• Conceptual literature review: This review synthesizes and integrates theories and concepts from multiple sources to provide a new perspective on a particular topic. It aims to provide a theoretical framework for understanding a particular research question.
• Rapid literature review: This is a quick review that provides a snapshot of the current state of knowledge on a specific research question or topic. It is often used when time and resources are limited.
• Thematic literature review : This review identifies and analyzes common themes and patterns across a body of literature on a particular topic. It aims to provide a comprehensive overview of the literature and identify key themes and concepts.
• Realist literature review: This review is often used in social science research and aims to identify how and why certain interventions work in certain contexts. It takes into account the context and complexities of real-world situations.
• State-of-the-art literature review : This type of review provides an overview of the current state of knowledge in a particular field, highlighting the most recent and relevant research. It is often used in fields where knowledge is rapidly evolving, such as technology or medicine.
• Integrative literature review: This type of review synthesizes and integrates findings from multiple studies on a particular topic to identify patterns, themes, and gaps in the literature. It aims to provide a comprehensive understanding of the current state of knowledge on a particular topic.
• Umbrella literature review : This review is used to provide a broad overview of a large and diverse body of literature on a particular topic. It aims to identify common themes and patterns across different areas of research.
• Historical literature review: This type of review examines the historical development of research on a particular topic or research question. It aims to provide a historical context for understanding the current state of knowledge on a particular topic.
• Problem-oriented literature review : This review focuses on a specific problem or issue and examines the literature to identify potential solutions or interventions. It aims to provide practical recommendations for addressing a particular problem or issue.
• Mixed-methods literature review : This type of review combines quantitative and qualitative methods to synthesize and analyze the available literature on a particular topic. It aims to provide a more comprehensive understanding of the research question by combining different types of evidence.

Parts of Literature Review

Parts of a literature review are as follows:

Introduction

The introduction of a literature review typically provides background information on the research topic and why it is important. It outlines the objectives of the review, the research question or hypothesis, and the scope of the review.

Literature Search

This section outlines the search strategy and databases used to identify relevant literature. The search terms used, inclusion and exclusion criteria, and any limitations of the search are described.

Literature Analysis

The literature analysis is the main body of the literature review. This section summarizes and synthesizes the literature that is relevant to the research question or hypothesis. The review should be organized thematically, chronologically, or by methodology, depending on the research objectives.

Critical Evaluation

Critical evaluation involves assessing the quality and validity of the literature. This includes evaluating the reliability and validity of the studies reviewed, the methodology used, and the strength of the evidence.

The conclusion of the literature review should summarize the main findings, identify any gaps in the literature, and suggest areas for future research. It should also reiterate the importance of the research question or hypothesis and the contribution of the literature review to the overall research project.

The references list includes all the sources cited in the literature review, and follows a specific referencing style (e.g., APA, MLA, Harvard).

How to write Literature Review

Here are some steps to follow when writing a literature review:

• Define your research question or topic : Before starting your literature review, it is essential to define your research question or topic. This will help you identify relevant literature and determine the scope of your review.
• Conduct a comprehensive search: Use databases and search engines to find relevant literature. Look for peer-reviewed articles, books, and other academic sources that are relevant to your research question or topic.
• Evaluate the sources: Once you have found potential sources, evaluate them critically to determine their relevance, credibility, and quality. Look for recent publications, reputable authors, and reliable sources of data and evidence.
• Organize your sources: Group the sources by theme, method, or research question. This will help you identify similarities and differences among the literature, and provide a structure for your literature review.
• Analyze and synthesize the literature : Analyze each source in depth, identifying the key findings, methodologies, and conclusions. Then, synthesize the information from the sources, identifying patterns and themes in the literature.
• Write the literature review : Start with an introduction that provides an overview of the topic and the purpose of the literature review. Then, organize the literature according to your chosen structure, and analyze and synthesize the sources. Finally, provide a conclusion that summarizes the key findings of the literature review, identifies gaps in knowledge, and suggests areas for future research.
• Edit and proofread: Once you have written your literature review, edit and proofread it carefully to ensure that it is well-organized, clear, and concise.

Examples of Literature Review

Here’s an example of how a literature review can be conducted for a thesis on the topic of “ The Impact of Social Media on Teenagers’ Mental Health”:

• Start by identifying the key terms related to your research topic. In this case, the key terms are “social media,” “teenagers,” and “mental health.”
• Use academic databases like Google Scholar, JSTOR, or PubMed to search for relevant articles, books, and other publications. Use these keywords in your search to narrow down your results.
• Evaluate the sources you find to determine if they are relevant to your research question. You may want to consider the publication date, author’s credentials, and the journal or book publisher.
• Begin reading and taking notes on each source, paying attention to key findings, methodologies used, and any gaps in the research.
• Organize your findings into themes or categories. For example, you might categorize your sources into those that examine the impact of social media on self-esteem, those that explore the effects of cyberbullying, and those that investigate the relationship between social media use and depression.
• Synthesize your findings by summarizing the key themes and highlighting any gaps or inconsistencies in the research. Identify areas where further research is needed.
• Use your literature review to inform your research questions and hypotheses for your thesis.

For example, after conducting a literature review on the impact of social media on teenagers’ mental health, a thesis might look like this:

“Using a mixed-methods approach, this study aims to investigate the relationship between social media use and mental health outcomes in teenagers. Specifically, the study will examine the effects of cyberbullying, social comparison, and excessive social media use on self-esteem, anxiety, and depression. Through an analysis of survey data and qualitative interviews with teenagers, the study will provide insight into the complex relationship between social media use and mental health outcomes, and identify strategies for promoting positive mental health outcomes in young people.”

Reference: Smith, J., Jones, M., & Lee, S. (2019). The effects of social media use on adolescent mental health: A systematic review. Journal of Adolescent Health, 65(2), 154-165. doi:10.1016/j.jadohealth.2019.03.024

Reference Example: Author, A. A., Author, B. B., & Author, C. C. (Year). Title of article. Title of Journal, volume number(issue number), page range. doi:0000000/000000000000 or URL

Applications of Literature Review

some applications of literature review in different fields:

• Social Sciences: In social sciences, literature reviews are used to identify gaps in existing research, to develop research questions, and to provide a theoretical framework for research. Literature reviews are commonly used in fields such as sociology, psychology, anthropology, and political science.
• Natural Sciences: In natural sciences, literature reviews are used to summarize and evaluate the current state of knowledge in a particular field or subfield. Literature reviews can help researchers identify areas where more research is needed and provide insights into the latest developments in a particular field. Fields such as biology, chemistry, and physics commonly use literature reviews.
• Health Sciences: In health sciences, literature reviews are used to evaluate the effectiveness of treatments, identify best practices, and determine areas where more research is needed. Literature reviews are commonly used in fields such as medicine, nursing, and public health.
• Humanities: In humanities, literature reviews are used to identify gaps in existing knowledge, develop new interpretations of texts or cultural artifacts, and provide a theoretical framework for research. Literature reviews are commonly used in fields such as history, literary studies, and philosophy.

Role of Literature Review in Research

Here are some applications of literature review in research:

• Identifying Research Gaps : Literature review helps researchers identify gaps in existing research and literature related to their research question. This allows them to develop new research questions and hypotheses to fill those gaps.
• Developing Theoretical Framework: Literature review helps researchers develop a theoretical framework for their research. By analyzing and synthesizing existing literature, researchers can identify the key concepts, theories, and models that are relevant to their research.
• Selecting Research Methods : Literature review helps researchers select appropriate research methods and techniques based on previous research. It also helps researchers to identify potential biases or limitations of certain methods and techniques.
• Data Collection and Analysis: Literature review helps researchers in data collection and analysis by providing a foundation for the development of data collection instruments and methods. It also helps researchers to identify relevant data sources and identify potential data analysis techniques.
• Communicating Results: Literature review helps researchers to communicate their results effectively by providing a context for their research. It also helps to justify the significance of their findings in relation to existing research and literature.

Purpose of Literature Review

Some of the specific purposes of a literature review are as follows:

• To provide context: A literature review helps to provide context for your research by situating it within the broader body of literature on the topic.
• To identify gaps and inconsistencies: A literature review helps to identify areas where further research is needed or where there are inconsistencies in the existing literature.
• To synthesize information: A literature review helps to synthesize the information from multiple sources and present a coherent and comprehensive picture of the current state of knowledge on the topic.
• To identify key concepts and theories : A literature review helps to identify key concepts and theories that are relevant to your research question and provide a theoretical framework for your study.
• To inform research design: A literature review can inform the design of your research study by identifying appropriate research methods, data sources, and research questions.

Characteristics of Literature Review

Some Characteristics of Literature Review are as follows:

• Identifying gaps in knowledge: A literature review helps to identify gaps in the existing knowledge and research on a specific topic or research question. By analyzing and synthesizing the literature, you can identify areas where further research is needed and where new insights can be gained.
• Establishing the significance of your research: A literature review helps to establish the significance of your own research by placing it in the context of existing research. By demonstrating the relevance of your research to the existing literature, you can establish its importance and value.
• Informing research design and methodology : A literature review helps to inform research design and methodology by identifying the most appropriate research methods, techniques, and instruments. By reviewing the literature, you can identify the strengths and limitations of different research methods and techniques, and select the most appropriate ones for your own research.
• Supporting arguments and claims: A literature review provides evidence to support arguments and claims made in academic writing. By citing and analyzing the literature, you can provide a solid foundation for your own arguments and claims.
• I dentifying potential collaborators and mentors: A literature review can help identify potential collaborators and mentors by identifying researchers and practitioners who are working on related topics or using similar methods. By building relationships with these individuals, you can gain valuable insights and support for your own research and practice.
• Keeping up-to-date with the latest research : A literature review helps to keep you up-to-date with the latest research on a specific topic or research question. By regularly reviewing the literature, you can stay informed about the latest findings and developments in your field.

Advantages of Literature Review

There are several advantages to conducting a literature review as part of a research project, including:

• Establishing the significance of the research : A literature review helps to establish the significance of the research by demonstrating the gap or problem in the existing literature that the study aims to address.
• Identifying key concepts and theories: A literature review can help to identify key concepts and theories that are relevant to the research question, and provide a theoretical framework for the study.
• Supporting the research methodology : A literature review can inform the research methodology by identifying appropriate research methods, data sources, and research questions.
• Providing a comprehensive overview of the literature : A literature review provides a comprehensive overview of the current state of knowledge on a topic, allowing the researcher to identify key themes, debates, and areas of agreement or disagreement.
• Identifying potential research questions: A literature review can help to identify potential research questions and areas for further investigation.
• Avoiding duplication of research: A literature review can help to avoid duplication of research by identifying what has already been done on a topic, and what remains to be done.
• Enhancing the credibility of the research : A literature review helps to enhance the credibility of the research by demonstrating the researcher’s knowledge of the existing literature and their ability to situate their research within a broader context.

Limitations of Literature Review

Limitations of Literature Review are as follows:

• Limited scope : Literature reviews can only cover the existing literature on a particular topic, which may be limited in scope or depth.
• Publication bias : Literature reviews may be influenced by publication bias, which occurs when researchers are more likely to publish positive results than negative ones. This can lead to an incomplete or biased picture of the literature.
• Quality of sources : The quality of the literature reviewed can vary widely, and not all sources may be reliable or valid.
• Time-limited: Literature reviews can become quickly outdated as new research is published, making it difficult to keep up with the latest developments in a field.
• Subjective interpretation : Literature reviews can be subjective, and the interpretation of the findings can vary depending on the researcher’s perspective or bias.
• Lack of original data : Literature reviews do not generate new data, but rather rely on the analysis of existing studies.
• Risk of plagiarism: It is important to ensure that literature reviews do not inadvertently contain plagiarism, which can occur when researchers use the work of others without proper attribution.

About the author

Muhammad Hassan

Researcher, Academic Writer, Web developer

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Introduction to Research Process: Literature Review Steps

When seeking information for a literature review or for any purpose, it helps to understand information-seeking as a process that you can follow. 5 Each of the six (6) steps has its own section in this web page with more detail. Do (and re-do) the following six steps:

1. Define your topic. The first step is defining your task -- choosing a topic and noting the questions you have about the topic. This will provide a focus that guides your strategy in step II and will provide potential words to use in searches in step III.

2. Develop a strategy. Strategy involves figuring out where the information might be and identifying the best tools for finding those types of sources. The strategy section identifies specific types of research databases to use for specific purposes.

3. Locate the information . In this step, you implement the strategy developed in II in order to actually locate specific articles, books, technical reports, etc.

4. Use and Evaluate the information. Having located relevant and useful material, in step IV you read and analyze the items to determine whether they have value for your project and credibility as sources.

5. Synthesize. In step V, you will make sense of what you've learned and demonstrate your knowledge. You will thoroughly understand, organize and integrate the information --become knowledgeable-- so that you are able to use your own words to support and explain your research project and its relationship to existing research by others.

6. Evaluate your work. At every step along the way, you should evaluate your work. However, this final step is a last check to make sure your work is complete and of high quality.

Continue below to begin working through the process.

5. Eisenberg, M. B., & Berkowitz, R. E. (1990). Information Problem-Solving: the Big Six Skills Approach to Library & Information Skills Instruction . Norwood, NJ: Ablex Publishing.

1. Define your topic.

I. Define your topic

A.  Many students have difficulty selecting a topic. You want to find a topic you find interesting and will enjoy learning more about.

B.   Students often select a topic that is too broad.  You may have a broad topic in mind initially and will need to narrow it.

1. To help narrow a broad topic :

a. Brainstorm.  

1). Try this technique for brainstorming to narrow your focus.   

a) Step 1.  Write down your broad topic.

b) Step 2. Write down a "specific kind" or "specific aspect" of the topic you identified in step 1.  

c) Step 3. Write down an aspect  --such as an attribute or behavior-- of the "specific kind" you identified in step 2.  

d) Step 4.  Continue to add  levels of specificity as needed to get to a focus that is manageable. However, you may want to begin researching the literature before narrowing further to give yourself the opportunity to explore what others are doing and how that might impact the direction that you take for your own research.                     

2) Three examples of using the narrowing technique. These examples start with very, very broad topics, so the topic at step 3 or 4 in these examples would be used for a preliminary search in the literature in order to identify a more specific focus.  Greater specificity than level 3 or 4 will ultimately be necessary for developing a specific research question. And we may discover in our preliminary research that we need to alter the direction that we originally were taking.

a) Example 1.      

             Step 1. information security

                      Step  2. protocols

                              Step 3.  handshake protocol

            Brainstorming has brought us to focus on the handshake protocol.

b) Example 2.  

            Step 1. information security

                     Step 2. single sign-on authentication

                              Step 3.  analyzing

                                       Step 4. methods

            Brainstorming has brought us to focus on methods for analyzing the security of single sign-on authentication

c) Example 3.  The diagram below is an example using the broad topic of "software" to show two potential ways to begin to narrow the topic. 

C. Once you have completed the brainstorming process and your topic is more focused, you can do preliminary research to help you identify a specific research question . 

1) Examine overview sources such as subject-specific encyclopedias and textbooks that are likely to break down your specific topic into sub-topics and to highlight core issues that could serve as possible research questions. [See section II. below on developing a strategy to learn how to find these encyclopedias]

2). Search the broad topic in a research database that includes scholarly journals and professional magazines (to find technical and scholarly articles) and scan recent article titles for ideas. [See section II. below on developing a strategy to learn how to find trade and scholarly journal articles]

D. Once you have identified a research question or questions, ask yourself what you need to know to answer the questions. For example,

1. What new knowledge do I need to gain?

2. What has already been answered by prior research of other scholars?

E.  Use the answers to the questions in C. to identify what words  to use to describe the topic when you are doing searches.

1. Identify key words

a.  For example , if you are investigating "security audits in banking", key terms to combine in your searches would be: security, audits, banking.

2.  Create a list of alternative ways of referring to a key word or phrase

a.For example , "information assurance" may be referred to in various ways such as: "information assurance," "information security," and "computer security."

b. Use these alternatives when doing searches.

3. As you are searching, pay attention to how others are writing about the topic and add new words or phrases to your searches if appropriate.

2. Develop a strategy.

II. Develop a strategy for finding the information. 

A. Start by considering what types of source might contain the information you need .  Do you need a dictionary for definitions? a directory for an address? the history of a concept or technique that might be in a book or specialized encyclopedia? today's tech news in an online tech magazine or newspaper?  current research in a journal article? background information that might be in a specialized encyclopedia? data or statistics from a specific organization or website?  Note that you will typically have online access to these source types.

B. This section provides a description of some of the common types of information needed for research.  

1. For technical and business analysis , look for articles in technical and trade magazines . These articles are written by information technology professionals to help other IT professionals do their jobs better. Content might include news on new developments in hardware or software, techniques, tools, and practical advice. Technical journals are also likely to have product ads relevant to information technology workers and to have job ads. Examples iof technical magazines include Network Computing and IEEE Spectrum .

2. To read original research studies , look for articles in scholarly journals and conference proceedings . They will provide articles written by  information technology professionals who are reporting original research; that is, research that has been done by the authors and is being reported for the first time. The audience for original research articles is other information technology scholars and professionals. Examples of scholarly journals include Journal of Applied Security Research , Journal of Management Information Systems , IEEE Transactions on Computers , and ACM Transactions on Information and System Security .

3. For original research being reported to funding agencies , look for technical reports on agency websites. Technical reports are researcher reports to funding agencies about progress on or completion of research funded by the agency.

4. For in-depth, comprehensive information on a topic , look for book-length volumes . All chapters in the book might be written by the same author(s) or might be a collection of separate papers written by different authors.

5. To learn about an unfamiliar topic , use textbooks ,  specialized encyclopedias and handbooks to get get overviews of topics, history/background, and key issues explained.

6. For instructions for hardware, software, networking, etc., look for manuals  that provide step-by-step instructions.

7. For technical details about inventions (devices, instruments, machines), look for patent documents .

C.   NOTE -  In order to search for and find original research studies,  it will help if you  understand  how information is produced, packaged  and  communicated  within your profession. This is explained in the tab  "Research Communication: Graphic."

3. Locate the information.

III. Locate the information

A. Use search tools designed to find the sources you want.  Types of sources were described in section II. above. 

Always feel free to Ask a librarian for assistance when you have questions about where and how locate the information you need.

B. Evaluate the search results (no matter where you find the information)

1. Evaluate the items you find using at least these 5 criteria:

a. accuracy -- is the information reliable and error free?

1) Is there an editor or someone who verifies/checks the information?

2) Is there adequate documentation: bibliography, footnotes, credits?

3) Are the conclusions justified by the information presented?

b. authority -- is the source of the information reputable?

1) How did you find the source of information: an index to edited/peer-reviewed material, in a bibliography from a published article, etc.?

2) What type of source is it: sensationalistic, popular, scholarly?

c. objectivity -- does the information show bias?

1) What is the purpose of the information: to inform, persuade, explain, sway opinion, advertise?

2) Does the source show political or cultural biases?

d. currency -- is the information current? does it cover the time period you need?

e. coverage -- does it provide the evidence or information you need?

2. Is the search producing the material you need? -- the right content? the right quality? right time period? right geographical location? etc. If not, are you using

a. the right sources?

b. the right tools to get to the sources?

c. are you using the right words to describe the topic?

3. Have you discovered additional terms that should be searched? If so, search those terms.

4. Have you discovered additional questions you need to answer? If so, return to section A above to begin to answer new questions.

4. Use and evaluate the information.

IV. Use the information.

A. Read, hear or view the source

1. Evaluate: Does the material answer your question(s)? -- right content? If not, return to B.

2. Evaluate: Is the material appropriate? -- right quality? If not, return to B.

B. Extract the information from the source : copy/download information, take notes, record citation, keep track of items using a citation manager.

1. Note taking (these steps will help you when you begin to write your thesis and/or document your project.):

a. Write the keywords you use in your searches to avoid duplicating previous searches if you return to search a research database again. Keeping track of keywords used will also save you time if your search is interrupted or you need return and do the search again for some other reason. It will help you remember which search terms worked successfully in which databases

b. Write the citations or record the information needed to cite each article/document you plan to read and use, or make sure that any saved a copy of the article includes all the information needed to cite it. Some article pdf files may not include all of the information needed to cite, and it's a waste of your valuable time to have to go back to search and find the items again in order to be able to cite them. Using citation management software such as EndNote will help keep track of citations and help create bibliographies for your research papers.

c. Write a summary of each article you read and/or why you want to use it.

5. Synthesize.

V. Synthesize.

A. Organize and integrate information from multiple sources

B. Present the information (create report, speech, etc. that communicates)

C. Cite material using the style required by your professor or by the venue (conference, publication, etc.). For help with citation styles, see  Guide to Citing Sources .  A link to the citing guide is also available in the "Get Help" section on the left side of the Library home page

6. Evaluate your work.

VI. Evaluate the paper, speech, or whatever you are using to communicate your research.

A. Is it effective?

B. Does it meet the requirements?

C. Ask another student or colleague to provide constructive criticism of your paper/project.

• << Previous: Research Communication Graphic
• Next: Search techniques >>
• Last Updated: Apr 15, 2024 3:27 PM
• URL: https://library.dsu.edu/graduate-research

Chapter Twelve: Positing a Thesis Statement and Composing a Title / Defining Key Terms

Defining Key Terms

You are viewing the first edition of this textbook. a second edition is available – please visit the latest edition for updated information..

Earlier in this course, we discussed how to conduct a library search using key terms. Here we discuss how to present key terms. Place yourself in your audience’s position and try to anticipate their need for information. Is your audience composed mostly of novices or professionals? If they are novices, you will need to provide more definition and context for your key concepts and terms.

Because disciplinary knowledge is filled with specialized terms, an ordinary dictionary is of limited value. Disciplines like psychology, cultural studies, and history use terms in ways that are often different from the way we communicate in daily life. Some disciplines have their own dictionaries of key terms. Others may have terms scattered throughout glossaries in important primary texts and textbooks.

Key terms are the “means of exchange” in disciplines. You gain entry into the discussion by demonstrating how well you know and understand them. Some disciplinary keywords can be tricky because they mean one thing in ordinary speech but can mean something different in the discipline. For instance, in ordinary speech, we use the word  shadow  to refer to a darker area produced by an object or person between a light source and a surface. In Jungian psychology,  shadow  refers to the unconscious or unknown aspects of a personality. Sometimes there is debate within a discipline about what key terms mean or how they should be used.

To avoid confusion, define all key terms in your paper before you begin a discussion about them. Even if you think your audience knows the definition of key terms, readers want to see how  you  understand the terms before you move ahead. If a definition is contested—meaning different writers define the term in different ways—make sure you acknowledge these differences and explain why you favor one definition over the others. Cite your sources when presenting key terms and concepts.

Key Takeaways

Strategies for Conducting Literary Research Copyright © 2021 by Barry Mauer & John Venecek is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.

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17 strong academic phrases to write your literature review (+ real examples)

A well-written academic literature review not only builds upon existing knowledge and publications but also involves critical reflection, comparison, contrast, and identifying research gaps. The following 17 strong academic key phrases can assist you in writing a critical and reflective literature review.

Academic key phrases to present existing knowledge in a literature review

The topic has received significant interest within the wider literature..

Example: “ The topic of big data and its integration with AI has received significant interest within the wider literature .” ( Dwivedi et al. 2021, p. 4 )

The topic gained considerable attention in the academic literature in…

Studies have identified….

Example: “ Studies have identified the complexities of implementing AI based systems within government and the public sector .” ( Dwivedi et al. 2021, p. 6 )

Researchers have discussed…

Recent work demonstrated that….

Example: “Recent work demonstrated that dune grasses with similar morphological traits can build contrasting landscapes due to differences in their spatial shoot organization.” ( Van de Ven, 2022 et al., p. 1339 )

Existing research frequently attributes…

Prior research has hypothesized that…, prior studies have found that….

Example:  “ Prior studies have found that court-referred individuals are more likely to complete relationship violence intervention programs (RVIP) than self-referred individuals. ” ( Evans et al. 2022, p. 1 )

Academic key phrases to contrast and compare findings in a literature review

While some scholars…, others…, the findings of scholar a showcase that… . scholar b , on the other hand, found….

Example: “ The findings of Arinto (2016) call for administrators concerning the design of faculty development programs, provision of faculty support, and strategic planning for online distance learning implementation across the institution. Francisco and Nuqui (2020) on the other hand found that the new normal leadership is an adaptive one while staying strong on their commitment. ” ( Asio and Bayucca, 2021, p. 20 )

Interestingly, all the arguments refer to…

This argument is similar to….

If you are looking to elevate your writing and editing skills, I highly recommend enrolling in the course “ Good with Words: Writing and Editing Specialization “, which is a 4 course series offered by the University of Michigan. This comprehensive program is conveniently available as an online course on Coursera, allowing you to learn at your own pace. Plus, upon successful completion, you’ll have the opportunity to earn a valuable certificate to showcase your newfound expertise!

Academic key phrases to highlight research gaps in a literature review

Yet, it remains unknown how…, there is, however, still little research on…, existing studies have failed to address….

Example: “ University–industry relations (UIR) are usually analysed by the knowledge transfer channels, but existing studies have failed to address what knowledge content is being transferred – impacting the technology output aimed by the partnership.”  (Dalmarco et al. 2019, p. 1314 )

Several scholars have recommended to move away…

New approaches are needed to address…, master academia, get new content delivered directly to your inbox, 26 powerful academic phrases to write your introduction (+ real examples), 13 awesome academic phrases to write your methodology (+ real examples), related articles, 10 tips on how to use reference management software smartly and efficiently, separating your self-worth from your phd work, how to introduce yourself in a conference presentation (in six simple steps), how to write effective cover letters for a paper submission.

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Progressive trend, conceptual terminology, and future directions of green façade research: A review of literature in 2010–2023

• Original Paper
• Published: 02 September 2024

Cite this article

• Y. Cui 1 , 2 ,
• J. Tang 3 &
• B.-J. He 2 , 4 , 5  

Climate change and urbanization have caused environmental problems to cities, making it critical to build a low-carbon, resilient, and sustainable urban environment. Green façade (GFA) is an important nature-based solution for implementation by exploring urban vertical space. GFA is often expected to meet versatile needs across different fields, but existing literature has not well documented the evolution of green façade research and future directions. Accordingly, this study examined GFA studies in 2010–2023 through a review to identify progressive trends, conceptual terminology, knowledge gaps, and future research directions. Overall, the GFA could be described by 46 additional terms given structure, vegetation, and technique properties. GFA research has evolved into transdisciplinary research, but mainly includes four clusters: (1) urban greening and sustainability; (2) energy saving mechanism and associated factors; (3) green infrastructure and cooling benefits; and (4) modelling and simulation for heat island mitigation and microclimate regulation. However, the ecological properties, lighting, and acoustic performance of GFA have scarcely been analyzed. Europe and China were key contributors of relevant literature, and there was strong co-authorship among authors from an organization, region, or country. Future efforts should focus on (1) verification and quantification of GFA environmental, ecological, and health benefits, (2) technical needs, economic benefits, social acceptance and support, and policy formation for promotion, (3) development of efficient and tangible numerical models and GFA typology for parametric analysis, and (4) promotion of inter-department, inter-organization, and inter-regional collaboration. Overall, this study enhances GFA understanding to enable the transformation from research to practice.

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Acknowledgements

Authors would like to appreciate the valuable comments from sessional chairs of 4th International Conference on Urban Climate and Urban Design in Xi’an, China.

This study is supported by the National Natural Science Foundation of China (No. 42301339), the Fundamental Research Funds for the Central Universities (Grant No. 2024CDJXY014), the China Meteorological Administration “Research on value realization of climate ecological products” Youth Innovation Team Project (No. CMA2024QN15), and Chongqing Natural Science Foundation Project (No. CSTB2024NSCQ-MSX0670).

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Y. Cui & B.-J. He

School of Urban Planning and Design, Shenzhen Graduate School, Peking University, Shenzhen, 518055, China

Institute for Smart City of Chongqing University in Liyang, Chongqing University, Liyang, Jiangsu, 213300, China

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Yi Cui: Conceptualization, Formal analysis, Investigation, Methodology, Visualization, Writing – original draft. Junqing Tang: Conceptualization, Investigation, Methodology, Resources, and Writing – review and editing. Bao-Jie He: Conceptualization, Formal analysis, Funding acquisition, Investigation, Methodology, Supervision, Writing – original draft, and writing – review and editing.

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Cui, Y., Tang, J. & He, BJ. Progressive trend, conceptual terminology, and future directions of green façade research: A review of literature in 2010–2023. Int. J. Environ. Sci. Technol. (2024). https://doi.org/10.1007/s13762-024-06030-8

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Published : 02 September 2024

DOI : https://doi.org/10.1007/s13762-024-06030-8

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Mixed reality in clinical settings for pediatric patients and their families: a literature review.

1. Introduction

1.1. importance of new technologies in health and education, 1.2. definitions and distinctions between ar, vr, and mr, 1.3. conceptual challenges and frameworks, 1.4. technological advancements and applications, 1.5. the role of ar and mr in modern healthcare and education, 1.6. psychological and physical risks of ar and vr, 1.7. gaps in research and the need for focused mr interventions, 2. materials and methods, 2.1. identification, 2.2. screening and eligibility, 2.3. included articles, 3.1. overview of included studies, 3.1.1. search results, 3.1.2. study characteristics, 3.2. general characteristics of the studies, 3.2.1. methods, 3.2.2. study population, 3.3. description of the interventions, 3.3.1. clinical settings of the mr application, 3.3.2. mr devices and software, 3.3.3. mr-based interventions.

• Early Adoption in Pain Management: Mott et al. [ 43 ], in 2008, represented the early adoption of MR in pediatric care. A child could visualize a 3D animation character from multiple angles in an MR system with audio narration, which made the child perform tasks. This highlights MR’s application in pain management and its ability to improve patient experiences in medical settings.
• Developmental and Educational Tools: By 2015, Bai et al. [ 38 ] established a setting for patients playing with augmented toys in a mirror MR display to improve and learn how to pretend to play, a crucial skill for autistic children. This showed the application of AR as a tool for social and cognitive development in children with ASD, promoting interaction and engagement. Similarly, a study by Calle-Bustos et al. [ 36 ] revealed MR’s role in interactive education for chronic health conditions, such as diabetes mellitus. An Android device overlaying MR food on a real dish was used in an AR game to support therapeutic education for children with diabetes mellitus, significantly contributing to self-management education in pediatric diabetes.
• Anxiety Reduction and Advanced MR Applications: In 2020, studies by Tait et al. [ 34 ] and Bray et al. [ 35 ] exemplified the maturity of MR technologies. Tait et al. used a printed storybook and an MR-enabled iPad program overlaying MR graphics, animations, and a chatbot with embedded interactive quizzes for information evaluation. Bray et al. employed the preloaded iPad Xploro ® , a digital therapeutic (DTx) platform that adopts AR, gameplay, and artificial intelligence, providing information on health environments, key health staff, and hospital equipment. Another study by Libaw et al. [ 37 ] in 2020 furthered the application of MR in clinical settings by applying the AR “Jenny the Robot” distraction technique during mask induction to encourage patients to take deep breaths.
• Social and Communication Skills Enhancement: Extracted from the primary study of Karami et al. [ 32 ], five individual studies on ASD conducted between 2015 and 2018 applied MR interventions for various social and communication skill-enhancing purposes. In a study by Chen et al. [ 39 ], AR-based Video-Modeling with Storybook (ARVMS)—comprising seven sessions—was devised to learn the facial expressions and emotions of others in social situations.
• Integration with Therapeutic Methods: Other studies targeting children with ASD, such as those by Kurniawan [ 40 ] and Nubia et al. [ 41 ], showed a continued trend toward using MR for enhancing communication and social skills. Kurniawan developed the Picture Exchange Communication System with AR-based multimedia using visual aids in a more interactive format to improve the communication abilities of children with ASD. In contrast, Nubia et al. introduced the process and simulation of an MR-based pictogram recognition task to improve the attention process and the appearance of verbal language in participants with ASD.
• Innovative Smart Glasses Applications: Vahabzadeh et al. [ 42 ] illustrated the innovative use of smart glasses-based interventions. Specifically, they reported that Empowered Brain, a smart glasses-based social communication and behavioral intervention, was used to improve the duration of gaze at faces and reduce ADHD symptoms in children, adolescents, and young adults with ASD.

3.4. Outcomes

3.4.1. variables, 3.4.2. main effect, 4. discussion, 4.1. study design and methodological considerations, 4.2. intervention characteristics and technological implementation, 4.3. population characteristics and clinical settings, 4.4. functional outcomes and practical implications, 4.5. intervention settings, technological implementation, and functional outcomes, 4.6. interrelationships between functional outcomes, 4.7. family involvement, care continuity, and future research directions, 4.8. limitations and future research directions, 5. conclusions, conflicts of interest.

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Sin, J.E.; Kim, A.R. Mixed Reality in Clinical Settings for Pediatric Patients and Their Families: A Literature Review. Int. J. Environ. Res. Public Health 2024 , 21 , 1185. https://doi.org/10.3390/ijerph21091185

Sin JE, Kim AR. Mixed Reality in Clinical Settings for Pediatric Patients and Their Families: A Literature Review. International Journal of Environmental Research and Public Health . 2024; 21(9):1185. https://doi.org/10.3390/ijerph21091185

Sin, Jae Eun, and Ah Rim Kim. 2024. "Mixed Reality in Clinical Settings for Pediatric Patients and Their Families: A Literature Review" International Journal of Environmental Research and Public Health 21, no. 9: 1185. https://doi.org/10.3390/ijerph21091185

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• Published: 05 September 2024

A Lucas island model to analyse labour movement choice between cities based on personal characteristics

• Tiange Qi 1 ,
• Yuning Gao 2 &
• Yongjian Huang   ORCID: orcid.org/0009-0001-2870-4216 3  

Humanities and Social Sciences Communications volume  11 , Article number:  1138 ( 2024 ) Cite this article

Metrics details

The labour movement has been a key factor for cities’ development and caused regional inequality between cities. Although empirical studies have been conducted to investigate it, little theoretical evidence has been provided to find out the underlying mechanism. This paper describes and derives a Lucas-Prescott style island model to study the location choices of the heterogeneous agents by utilising endogenous technology growth, which in turn influences personal human capital growth. It leads to the U-shape curve of the inequality of wage income with the technology of these islands but not in terms of total income. In the extended two-goods model, the magnitude of the implications is increased by the impact of non-tradable goods price. Together with empirical research using the US census data, this paper finds that skilled labours with less endowed wealth tend to live in large cities for its high salary. On the other hand, those less-skilled but with more endowed wealth tend to live in cities with better environment, which drives up the price level of non-tradable goods in these cities. This explains the population concentration in the super cities and the high housing price-wage ratio in some beautiful cities, which provides theoretical basement for further empirical studies about labour movement in other cities

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Introduction and literature review.

Since the advent of the Industrial Revolution, urbanisation has become a common trend across the world and has accelerated a great deal over recent years. According to the World Bank, database Footnote 1 , the rate of worldwide urbanisation has risen from 34% to 37% from 1960 to 2022. This is underpinned by the fact that rates in developing countries such as Mexico have gone from 51% to 81% and in Brazil from 46% to 88% during that period. However, even developed countries such as US and UK have witnessed a rapid increase of the urbanisation rate, going from 79% to 83% and 79% to 84%, respectively within the last 20 years.

The concentration of population is a significant phenomenon for consideration during urbanisation. In specific countries, the population share of largest city to total urban population Footnote 2 is relatively high, such as in the UK (17%), Canada (20%), Mexico (21%), France (20%), Austria (23%), Japan (32%) and Chile (40%) when compared to Germany (5%) and US (7%). However, this percentage has been decreasing since 2000 in many major economies except for Austria and Canada, which have relatively lenient immigration policies. This population concentration brings about inequality, which is seldom addressed. Nord ( 1980 ) finds that with the increasing size of the city population, income equality produces a U-shaped curve, arguing that as the population immigrates to city, the occupational and wage structure of local labour market will change. Small cites lack infrastructure and sufficient size to support the types of business to distribute income. High-income business is monopolized at certain local enterprisers and immigrants have to enter the business with low income. As the city size increases, the improved infrastructure and demand provides capacity to different types of business and they provide higher salary to attract skilled immigrants, which would decrease inequality. However, Madden ( 2000 ) and Glaeser et al. ( 2009 ) point out inequality always increases with population. They find that in 2006, the elasticity of Metropolitan Statistical Area Footnote 3 ’s Gini coefficient to city population is 0.036 and highly significant in US cities by US Census data. Additionally, they find that the mean derives from the top 5% mean income in a Metropolitan Statistical Area in relation to the overall mean income within that Metropolitan Statistical Area is highly significant. What’s more, for high-productivity people, income is disproportionally positively correlated with the size of the city. They think that as population increases within the city, the market expands and the business, which requires high-skilled workers, will increase. This increases the demand for high-skilled workers and their wage return to human capital. At the same time, immigrants from Latin America, which are mainly low-skilled workers, worsens this wage inequality within the city. Wheeler ( 2001 ), Baum-Snow and Pavan ( 2009a ) prove the robustness of this positive effect. The additional premium gained by a greater number of productive people arises in every quintile of the income distribution, as well as the development of the city has a direct effect on inequality even if the effect of socio-economic composition is ignored. Behrens and Robert-Nicoud ( 2014 ) build a model, which links the size of the city to inequality and productivity. In addition to the view that the increase of city size will increase the skill premium, they also argue that urbanization will improve competitiveness and openness to business, which decreases the cost of logistics and transportation and therefore increases the price competition locally (as the price of shipping goods to customers or their nearby shops is low, the local goods’ advantages decrease). This will benefit the entrepreneurs which produce exported goods. And as only most productive companies export their goods, these companies will become richer, which increases inequality and productivity. Higher productivity will also increase the city size by attracting migrates, which is a cyclical effect. Castillo et al. ( 2020 ) notice that labour mobility will bring new knowledge to the companies, which benefits their productivity by knowledge diffusion, regardless of labour’s level of skills.

The core to addressing these facts is understanding the drive behind different kinds of labour movements in different cities. Lucas and Prescott ( 1978 ) argue that decisions concerning labour movement should balance in terms of the trade-off for the benefit of moving to a higher-wage company (as island in the model) and the loss of wages during the period of ‘searching for that company’. Therefore, they conclude that the technology heterogeneity between each island is the main drive behind unemployment as people have incentives to move to companies with higher technology to earn a higher wage, whereas those who are still searching for a better job contribute to unemployment. Then Coen-Pirani ( 2010 ) modifies the island model to include the use of land in the production function and land rent in income, applying it to analyse flow of labour between cities.

The theoretical rationale of this paper utilises the Lucas-Prescott model to address aspects of urbanisation, labour flow, and inequality. Rather than using a homogenised sense of labour in their model, this model introduces skill-heterogeneity between labour based on the model of Behrens and Robert-Nicoud ( 2014 ). Also, the model for this paper replaces land with capital as a complementing factor with labour to produce consumption goods. Additionally, both workers and capitalists are defined as agents. This is because land can be included in capital and it is also not the main factor for production in industrialised countries. In the UK, 57.5% of lands are used for the purpose of agriculture in 2018 (Ministry of Housing, Communities & Local Government, 2020 ), while the percentage of agriculture to UK GDP is only 0.61% (ONS, 2021 ). Introducing capital will add more flexibility and be more realistic. To address the facts of labour flow from large cities to cities that have beautiful natural landscapes, this paper also includes the utility of the quality of the environment, as it affects the movement of labour. Despite the wage mentioned above, another factor affecting job choice is environment (Feld et al., 2022 ). Chen et al. ( 2022 ) also find that the air pollution is responsible for large labour mobility in China: 10% air pollution will result in 2.8% population outflow in China in average. We therefore add the environmental factor in the labour’s utility function.

Our paper makes contributions in several aspects. Firstly, is contributes to the theoretical literatures about labour’s migration choice (Harris, 1970 ; Borjas, 1987 ; Zenou, 2008 ; Coen-Pirani, 2010 ; Chin and Cortes, 2015 ; Zhao, 2020 ; Aksoy and Poutvaara, 2021 ). Previous models address heterogeneous wage levels with homogeneous labours, such as McCall ( 1970 ) Research model where labours have a minimal wage to make them indifferent between accepting the job offer or waiting for a better job, which can also be used to explain unemployment rate. The Hopenhayn ( 1992 ) model addresses the entrance and exit mechanism of business in the labour market, of which the driving force is stochastic productivity of companies. The Aiyagari ( 1994 ) model analyses the matching process of labours with heterogeneous skill levels to homogeneous companies. The Krusell and Smith ( 1998 ) model combines the above two models, which incorporates a model with both heterogeneous labours and companies in terms of productivity. It finds the distribution of heterogeneous companies and their employees. However, these models do not consider the wealth as a factor in the matching process. We argue that the labour choice does not only depend on its human capital but also its asset, which complement their work, as the current research does not notice the negative effect of asset on the intention of labour to move for higher wage. Different from the mostly common search models, we introduce above where labour only care about consumption, our model is the first one to introduce environment to affect the labour choice. These two changes can explain the choices of different types of labours, not only in terms of the heterogeneous productivity but also the resources of the income to different cities.

Secondly, this paper constructs the distribution of labour in terms of workers’ talent and their endowed capital in cities with degrees of different technology and environment, which provides a theoretical support to the empirical work of cities’ wage differences, especially those of developing countries (Gong and Van Soest, 2002 ; Bargain and Kwenda, 2011 ; Buch et al., 2014 ; Cao et al., 2015 ). This is because the technology inequality between cities is server in developing countries and their industry structure means that technology development usually results in pollution, which will lead to higher rate of labour mobility.

Thirdly, this paper explains the price heterogeneity between cities due to the mobility of different labours. Van Nieuwerburgh and Weill ( 2010 ) propose an island model to analyse the effect of labour mobility on the housing price. They argue that the productivity is the determinant of labour mobility and wage level, which affect cities’ housing price, which is consistent with our research. However, the positive correlation between wage and housing price do not apply in some cities, which will be discussed later. Our model with the environmental factor, asset and connection between the tradable goods and non-tradable goods solve this problem. We conclude that even though wage difference due to the technology inequality is positively connected with the price level of non-tradable goods, labour’s mobility choice due to non-wage attributes plays an important role in the price level of non-tradable goods.

The remainder of this paper is organized as follows. Section “The baseline model” discusses the baseline model and establishes the equilibrium condition. And Section “Extended two-goods model” presents a more complicated version of the model, which allows for the inclusion of tradable and non-tradable goods to address the price of heterogeneity between different cities. While Section “Empirical analysis” carries out the simple empirical analysis, to support our model. Last, Section “Conclusion” concludes our paper.

The baseline model

Lucas-prescott model.

Within the Lucas-Prescott economy, people’s income comes from their wages and the rent of capital. At the beginning of the period, each agent is on an island. The shocks are then publicly realised, and people respond to them by deciding to stay or leave the island. If people decide to leave the island, they do not work during the period (but can still receive the interest of the capital) and will go to a new island at the beginning of the next period. If they choose to stay, they can receive both wage income and the rent of capital. The island economy system is a closed economy without any international trade and capital inflow and outflow. Empirically, the system can be seen as a large economy or each island can be seen as a political identity. The monetary policy is neutral and there is no rigidity i.e. it only considers a real term.

A recursive equilibrium with rational and infinite life agents is used in this paper and is a set of functions:

where z is the technology in the island; q is the quality of living in each island or the function of the environment; h is the human capital of each individual; k is the capital owned by each individual and ω ( h ,  k , ϑ| z ,  q ,  K ) is the number of people with human capital h , capital k and the speed of learning ϑ, which is the natural talent of each agent on the island with technology z , capital K and quality q .

μ ( z ,  q ,  ω ,  K )is the density of the island with technology z , quality q and number of people ω and total capital K . w ( ω ,  z ,  μ ,  q ,  K ) is the wage at the island and r ( μ ) is the rate of return to the capital. People can install their capital in each island without any barrier, which suggests that the return of capital for each island is the same. τ w and τ k are the tax rates of wage and capital return.

Each agent cares about both consumption and the quality with utility function. u ( c t , q t ) = ln( c t ) + ln( q t ), wher c t is the consumption at time t . People do not have disutility on labour and each one is endowed with 1 unit of labour in each period.

It satisfies:

\(v(\omega ,z,h,\mu ,q,k,\vartheta ,K)=\,\max \{{v}_{stay}(w,z,h,\mu ,q,k,\vartheta ,K),{v}_{leave}(k,h,\vartheta ,\mu )\}\) , which is the utility of the agent with h , ϑ, k at the island with ω z μ K q . He or she chooses the maximum between the utility of staying at the island or leaving the island at the start of each period.

is the utility of staying at the same island at the period. The agent chooses the investment to decide the capital next period k ’ to maximise the utility of consumption from return of the capital with depreciation rate δ k ∈ (0,1) plus the wage as well as the utility of environment and the expected discounted utility at the next period with discount rate β ∈ (0,1). The notation a’ suggests the variable a at next period.

is the utility of leaving the current island.

The agent is now on the way to search for new island. He or she chooses k ’ to get return from investment while the agent cannot receive the wage at the period and he or she enjoys the environment “on the way” \(\underline{{\rm{q}}}\) , which is lower than the environment of all islands. The agent also decreases the human capital with rate δ h ∈ (0,1).

suggests agent searches for an island to maximise the expected utility and arrives at that island at the start of next period.

z and h follow the growth path \(\dot{z}=\theta (\int h* {e(h,k,\vartheta {|z},q,\omega ,K){dh}\times {dk})}^{\lambda }{z}^{\phi }{z}_{n}^{\gamma }\) , which is the increase of technology and \(\dot{h}=\vartheta {h}^{\eta }{z}^{\kappa }\) is the increase of the human capital.

Where e ( h ,  k ,  ϑ | z ,  q ,  ω ,  K ) is the number of employed people with capital k, human capital h and speed of learning ϑ given the island with technology, quality, the number of people and total capital z ,  q ,  ω ,  K .

The structure of growth suggested by Romer ( 1986 ) will be used, which assumes that technology increase is the function of current technology, researchers in each island and ‘natural technology’ z n , growing constantly at g . It is also assumed that the proportion of human capital used for the research is constant. This is the reason for introducing θ .

It will be applied to human capital growth. Human capital growth is positively correlated to current human capital and the technology of the city. The inclusion of technology is because the human capital need grow faster when the worker works in a company aiming with higher productivity (Abel et al., 2012 ). The elasticity of researchers to technology growth λ , the elasticity of current technology to technology growth ϕ , the elasticity of nature technology to technology growth γ , the elasticity current human capital to human capital growth κ and the elasticity of technology to human capital growth η are constant and within the range of (0,1).

There is a production sector in each island, which hires human capital and capital with production function F(zH, K) , which is homogeneous with degree 1, to solve:

Given w ( ω ,  z ,  μ ,  q ) and r ( μ )

For consistency, each island i with z , q has:

Equilibrium

Taking First order condition wrt K and H for each island i:

The first order condition for capital is used to determine the allocation of capital in each island as ∀ i F 2 ( zH , K ) and is equal for each period.

We can now find the market clearing condition:

For each island with technology and quality z and q , the agents with capital and human capital k and h can choose to

If \({\nu }_{{stay}}(\omega ,z,h,\mu ,q,k,\vartheta ,K)\le {\upsilon }_{{leave}}(k,h,\vartheta ,\mu )\) , people with k and h leave the island and we have ν stay ( ω ,  z ,  h ,  μ ,  q ,  k ,  ϑ ,  K ) = υ leave ( k ,  h ,  ϑ ,  μ ) in equilibrium, people leave the island.

Therefore, we have

If ν stay ( ω ,  z ,  h ,  μ ,  q ,  k ,  ϑ ,  K ) > υ leave ( k ,  h ,  ϑ ,  μ ) and

None of these people come and leave the island. Therefore, we have ω ′( k ′, h ′, ϑ | z ′ ( ω , q , z ), q ′ ( μ ), K ′) = ω ( k , h , ϑ | z , q , K )

If people come to the island and we can pin down ω ′ by the condition

The model also obtains:

which is the density of the island’s next period with technology, quality and distribution of capital and human capital Δ z , Δ q , Δ ω

Steady state

In the traditional Lucas island model, there is a stochastic item in the technology and there is still labour movement in the steady state. However, the distribution in terms of the islands’ technology, production and labour is constant. However, as this model includes more complexity of technology and human capital growth, the existence of stochastic items will never reach a steady state in the model. Recall the growth of z depends on the z last period. If there is a stochastic item in the technology, the growth rate will never become constant. Therefore, for simplicity, our model does not include uncertainty and the steady state can simply be known as the population does change in each island, the technology and human capital grow as a constant rate and quality of environment is also constant. In the real world, it is apparently that it is impossible to reach such a steady state between cities because there are always labour with different levels of talents and wealth entering the market and retiring from the market. However, this model reveals a regulation of labour movement. Empirically, with the personal demography data, regressing their settlement choice with their demography, which is the topic of our future research also with deep empirical analysis, can prove this.

The steps to solving the steady state can be found in Appendix 1 .

The condition for steady state can be solved now:

Condition 1 – For agents with initial value of k 0 , h 0 , ϑ at the time of steady state, they will only be on the island with:

z 0 , q 0 ∈ { z 0 ,  q 0 | v stay ( z 0 ,  q 0 ,  k 0 ,  h 0 ,  ϑ ) ≥  v leave ( k 0 ,  h 0 ,  ϑ )}

Condition 2 – The sum of capital in each island should equal the sum of capital of each agent:

where ξ is the pre-defined unconditional distribution of k 0 and ϑ .

Condition 3 – With the same logic, for each island i, the human capital employed by the company should be equal to the sum of human capital in that island:

Condition 4 – \(\frac{{K}_{t}}{{z}_{t}{H}_{t}}\) is constant which can be solved by (3)

These four conditions suggest that given ξ and μ ( z 0 , q 0 ), there may be many steady state equilibriums if these conditions are satisfied. This is because condition 1 implies that for each pair of ( k 0 , ϑ ), we can always find the set of ( z 0 , q 0 ) of which island the agent can stay in. There can be many allocations of each agent to the corresponding islands if the remaining conditions are satisfied.

Switching from island A to island B increases the utility of quality \(\Delta {u}_{q}=\,\mathrm{ln}(\underline{q})+\frac{\beta \,\mathrm{ln}({q}_{B})}{1-\beta }-\frac{\mathrm{ln}({q}_{A})}{1-\beta }\) , which is constant. In terms of the utility of consumption, switching from one island to another with higher technology will decrease human capital and the level of equilibrium h 0 ( z B , ϑ ) > h 0 ( z A , ϑ ) at the time when the agent arrives at island B. Therefore, the agent needs time to reach the new equilibrium. For the human capital when the agent arrives at the island B, \(\dot{h}=\vartheta {h}^{\eta }{{z}_{B}}^{\kappa }\) , we use the first order Taylor approximation:

Where h * is steady state level of h ( z B , ϑ ) at the current time.

Multiply \(\frac{1}{{g}_{h}h}\) and substitute \(\vartheta {{h}^{* }}^{\eta -1}{{z}_{B}}^{\kappa }={g}_{h}\) :

Where g t is the growth rate of h , at time t .

We define that at the time of arriving at the island 0, the ratio of the agent’s human capital to the equilibrium level of human capital is \(\frac{(1+{g}_{k}){h}_{0}({z}_{B},\vartheta )}{(1+{\delta }_{k}){h}_{0}({z}_{A},\vartheta )}=\pi\) . Then we have:

Therefore, we can solve the time T when \(\frac{{g}_{T}}{{g}_{h}}=1\) if t ≥ T .

As we also know that in steady state 1 + g k = (1 + g h )(1 + g z ) and ln (1 + g z ) can be cancelled out in the consumption utility gain.

The consumption utility gain from switching island Δ u c is:

We are now able to find the locations of agents with different characteristics. We assume that island A is an island with relatively high quality but low technology and that island B is an island with relatively low quality but high technology. Switching from A to B has a positive utility gain from consumption and negative utility gain from quality i.e. Δ u c > 0, Δ u q < 0.

Proposition and their testing

Proposition 1. People with high capital and low speed of learning tend to stay in the island with better environment and people with low capital and high speed of learning tend to stay in the island with higher technology

The above algebra demonstrates that the consumption gain from island A to B is positively related to the speed of learning. As the utility change of consumption is positively related to the change of consumption, the agent who can learn quickly will receive greater benefit from switching island.

It is also noteworthy that the utility consumption is concave in the consumption, implying that the increase in utility related to the growth of consumption from a low level in likelihood will be more than the utility decrease brought about by switching from a high-quality island to a low-quality island, which is irrelevant to the level of wealth. The reason for this is that the initial level of capital does not affect the change of consumption that is caused by switching island while the initial level of consumption does affect the change of utility. In terms of concave utility, given the fixed change of consumption, the higher the initial level of consumption, the lower the change of utility will be.

Therefore, an agent with low capital that can learn rapidly will be more likely to switch to the island with high technology even though they might have to live in an island with the worse environment. Conversely, agents with high capital that learn slowly will gain less from switching to a high-technology island. They are less like to sacrifice the quality of the environment to earn a higher wage.

Proposition 2. People with high capital and high speed of learning or people with low capital and low speed of learning tend to stay in the island with balanced technology and environment

A high (low) level of capital has a negative (positive) effect on the utility gain while a high (low) speed of learning has a positive (negative) effect. Therefore, agents will balance the benefits of wages and quality and are more likely to locate themselves on an island where the level of technology and capital are relatively proportionate.

Proposition 1 could potentially explain the reason that people in the upper-middle economic class ‘escape’ from metropolitans. It could also partially explicate the reason for the high concentration of highly educated people and capital in larger cities. However, Proposition 2 alone is not enough to justify the correlation between inequality and urbanisation. Moreover, it also cannot interpret the reasons for labour concentration only occurring happens in particular countries. This suggests that as there are multiple steady-state equilibriums, different assumptions about the distribution of productive, capital and speed of learning could be added to ‘narrow’ the equilibriums of different countries. Initially, we should assume that the distribution of speed of learning follows a truncated normal distribution in each island from \([\underline{\vartheta },\bar{\vartheta }]\) and has the same mean and variance, which follows the setting of Pluchino et al. ( 2018 ) where the talent of people is randomly assigned. In terms of each level of initial capital owned by the individual, the conditional distribution of the speed of learning to capital follows the same normal distribution as well. We should note that two distributions are independent and it is because the endowment capital is decided by the nature at the time when the city firstly functions in our paper. For example, when migrates find a new continent or they build a new city in a forest, the endowment wealth is the nature resources they have at the time of settling down.

We now start from the economy with two islands A and B and z B > z A , q B < q A , which is consistent with what has already been discussed. It is evident that given ϑ , the net gain from switching A to B decreases with capital k . However, for the given k , we find that the part of Δ u c when t  >  T is:

As we know that \(h\left(z,\vartheta \right)={(\frac{\vartheta {z}^{\kappa }}{{g}_{h}})}^{\frac{1}{1-\eta }}\) , it equals:

which increases with ϑ

Also, as \(\frac{(1+{g}_{h}){h}_{0}({z}_{B},\vartheta )}{(1-{\delta }_{h}){h}_{0}({z}_{A},\vartheta )}=\pi\) , which is irrelevant of ϑ and, T and g t are irrelevant ϑ when t  <  T . Therefore, the degree to which the utility of consumption is different at each time before T , which is the same form after T , increases with ϑ . So we can conclude that with the same k , the willingness to move from A to B increases with ϑ .

Based on the analysis above, we can now produce a graph (Fig. 1 ), which demonstrates visually the location of agents for each k and ϑ .

For given k , Δ u c requires a higher level of ϑ to be equal to the fixed Δ u q . The shape of curve is convex and \(\frac{\partial \Delta {u}_{c}}{\partial k\partial \vartheta } \,>\, 0\) , which implies it needs an increasing marginal value of ϑ for higher level of k to keep the Δ u c constant.

The curve indicates that given the certain value of k , all agents have a speed of learning, of which the gain and loss from switching A to B is equal and below \(\bar{\vartheta }\) , the highest limit of talent, which is not depicted in the graph, but it is assumed that it is above the curve for every k .

As the distribution of ϑ is the same for each k in each island to begin with, we find that the higher the level of k , the fewer agents will be located in the island B, and the higher mean of ϑ for those who are located in the island B. This will lead to income polarisation as all the richest people in island B do not leave whilst the richest people in island A move to island B. This increases the overall number of people that have high wages and capital, and whose income is in the top quartile of income distribution.

With regards to people with lower capital, the lower bound of ϑ to be located in island B decreases, implying that the most impoverish people move to island B. However, as k increases, most people whose ϑ is not high enough will move to island A. These people tend to have an income within the quartile between the richest and poorest, therefore, income inequality becomes more pronounced than in the initial distribution for island B.

The main source of income for people that have a lower capital is their wages and if they do not relocate to the city with higher technological advancement, their consumption will be too low thus they will find it difficult to survive. Therefore, they will often move to chase higher wages even though the level of quality might be lower. The capital income of people who possess a lot capital of is high enough to satisfy their consumption needs; as such they might be more inclined to enjoy the higher quality of life afforded to them by living in a rural and/or seaside city. It is only the richest people whose wages are also high that will opt to stay where they are because they do not want to see a reduction in their income by moving as their wage makes up a significant part of their total income. Furthermore, wage income may not only be a wage given by an employer but can also refer to the income generated by the companies of entrepreneurs which is based in the city where the agent residents.

This could also be the reason that foreign immigrant is seen to gather in metropolitan areas. Migrant workers are generally seen as agents with a low level of capital. The lower bound of ϑ to be in the island B is low, as such most of this group will choose to locate in cities with higher technology. This is consistent with the empirical data gathered in UK where 35% of people who are born outside of the UK live in a capital city (ONS, 2021 ) and is also consistent with Gordon and Kaplanis’ ( 2014 ) research which argues that immigrants are the reason for the increase of low paid jobs in metropolitans.

The multiple islands economy will now be examined. No matter what the distribution of the ( z , q ) of the islands is, one island must be the best in terms of technology and the other in terms of equality. We will call them island B and A for consistence.

For υ leave ( k , ϑ ) in the steady state of every level of k and ϑ , it searches for islands with z , q to maximise

When desiring to move, agents will be able to find their corresponding ideal island and if we draw all the ( z , q ) sets on the 2-dimensional graph, the necessary condition for ideal islands is that they must lie on the northeast frontier (connecting all of the points, which has no points on the northeast side in Fig. 2 ). In terms of Island E and F, they cannot be ideal islands as there are islands with both a higher z and q .

The graph describes the islands with different environments and technologies. The ideal islands should be the ones on the frontier.

When comparing B and D, the lower bound of ϑ B ( k ) can be found above which the agent prefers B to D and below which the agent prefers B to D. Then we compare D and C and trace the lower bound of ϑ D ( k ) above which the agent prefers C to D and below which the agent prefers C to D. Again, going through the same steps, we can outline ϑ C ( k ) above which the agent prefers C to A and below which the agent prefers C to A. Therefore, as the agents are rational, which implies the transitivity of their preference, the ideal island of the agent with ϑ and k in the region [ ϑ x ( k ), ϑ y ( k )] is y . Moreover, as we know that the lower bound ϑ y ( k ) decreases with k , it is possible to draw the graph (Fig. 3 ) describing the ideal location of agents with different ϑ and k:

The areas in the graph are the ideal islands to settle down for the individuals with corresponding knowledge and wealth.

Agents that will move are now the focus of the research. As has been established, on the frontier, a higher quality island must be accompanied with lower levels technology. For each level of k and ϑ , the conclusion of the two islands economy for each two neighbour islands can be applied to find the ideal island for each agent. The agent with highest level of k and the island with highest level and second highest level of z is the starting point. For simplicity, we continue to use the six islands case (it can be applied to any number of islands with the only difference being the times of the comparison).

Given k , as an agent’s choice of an ideal island is determined solely by the speed at which the agent learns, their income is determined by it as well. This means that the analysis of the income distribution can be simplified to the speed of learning distribution.

However, for each region of y on each island, not all agents will move to their ideal island as the cost of moving and living there might be too high for them to afford i.e. Δ u c  + Δ u q  < 0. For each island i, the threshold value of \({\vartheta }_{y}^{i}\) can be calculated, where the agent is indifferent about whether they will move to island y or not ( y ≠ i ).

In other words, the Fig. 3 is different from Fig. 1 , as Fig. 3 indicates the island where the agent wants to move if the agent is forced to be 'on the way' to search for an island for one period and arrive to a island at the next period. This island is called 'ideal' island. Therefore, there are agents who want to stay at the current islands if they are not forced to move. \({\vartheta }_{y}^{i}\) is the threshold of talents of people in island i who are indifferent between moving to island y. \({\vartheta }_{y}^{i}(k)\) is actually the ϑ ( k ) of Fig. 1 .

For the neighbouring island i, \({z}_{i}\, > \,{z}_{y}= \,>\, {\vartheta }_{y}^{i} \,<\, {\vartheta }_{y}\) and \({z}_{i}\, < \,{z}_{y}= \,>\, {\vartheta }_{y}^{i} \,>\, {\vartheta }_{y}\) .

This is because in terms of the original island and the target island, the absolute value of Δ u c is positively correlated with ϑ . Moreover, moving to other islands incurs additional costs of utility; moving to islands with higher technology requires higher ϑ to gain more income and offset the costs. With the same logic, moving to a lower technology island will require lower ϑ to experience a smaller decrease in income. We also assume that \({\vartheta }_{y}^{i}\) is within the region y to ensure that there are agents moving to all other islands.

All the people in region B stay in island B and some of people from region B in other islands move to island B. Furthermore, there is an outflow of people from island B to other regions, which increases the proportion of region B people who are the richest on island B. With the same logic, island A faces a concentration of the poorest people as well as an outflow of people in other regions. In both island A and B, inequality is increased compared to their original states.

However, regarding island C and D, we see an outflow of both the richest and poorest people and inflow of middle-class people, which causes inequality to decrease.

The unattractive islands like E and F face a population outflow and only those who suffer a loss of utility because of bad quality and the loss of wages during moving which offsets the gain of moving to the ideal island will stay. The percentage of the population that stays is non-decreasing with z and q given the distribution of ( k , ϑ ) fixed.

The conclusion we can draw from that is that, for given k, wage inequality decreases then increases as the technology of the island also advances. Therefore, as the wage distribution starts out as the same (truncated normal), the total wage inequality also follows the same trend as the one conditional on k .

As k decreases, the area of region B increases, and the concentration of region B agents moving from other islands to island B also goes up. This leads to an ambiguous effect on inequality as it did for the high-technology island. For each k (i) the average income decreases as k decreases but (ii) the proportion of agents with capital k to the total number of agents in that island increases. It is impossible to know which effect dominant, therefore we also cannot know why the income distribution has shifted. The effects are the opposite for island A compared to those of B as k increases, but still the two effects conflict with each other.

Extended two-goods model

Description.

The difference compared to the baseline model is that we now have two consumption goods:

Tradable goods, which can be traded between islands, must have the same price for all islands, as such we can normalise the price as 1. They will be referred to as good A.

The non-tradable goods, which can only be consumed locally, will have different prices depending on the island. They will be called good B.

The utility of the agent now is

We now have Bellman equation for the agent:

The modification is that an agent can immediately arrive at any of the other islands without delay but can only start working during the next period.

z A and h follow the growth path \(\dot{{z}_{A}}=\theta {({H}_{A})}^{\lambda }{{z}_{A}}^{\phi }{{z}_{n}}^{\gamma }\) and \(\dot{h}=\vartheta {h}^{\eta }{{z}_{A}}^{\kappa }\) and H A is the human capital working to produce A. Following the deviation performed in part I, we have in steady state:

The technology of the non-tradable good z B is the same for all islands as it grows at the constant rate: \({g}_{{\rm{zB}}}={g}_{z}=\frac{1-\eta }{\left(1-\phi \right)\left(1-\eta \right)-\lambda \kappa }g\) , i.e. all technologies grow at the same rate in steady state.

There are two production sectors in each island for two goods. The sector of good A is the same, which is homogeneous with degree 1, to solve:

Given w ( ω , z A , μ , q ) and r ( μ )

The sector of good B, with its price p B ( ω , z A , μ , q ) given, is also homogeneous with degree 1 and it solves:

For consistence, in each island: \({H}_{A}+{H}_{B}=\int h* e(k,h,\vartheta |{z}_{A},q,\omega ){dkdhd}\vartheta\) and K A + K B = K

We solve the first conditions for two sectors and apply the law of one price on Appendix 2 .

We now can solve other conditions for steady state:

Condition 1 – Agents with initial value of k 0 , h 0 , ϑ at the time of steady state, will only be on the island with

Condition 2 – The sum of capital for each island should equal the sum of capital for each agent:

Condition 4 – At each island the total production of non-tradable goods is equal to their total consumption:

Similarly to part I, any distribution of ω and μ as well as satisfying the above conditions can suffice as the equilibrium, as such there are multiple equilibriums.

Compared with part I, the locations of labour based on the characteristics and the differing distributions of islands are comparable while people’s willingness to move to the higher quality cities is determined by the lower prices-wage ratio of their non-tradable goods. The region of area B and the concentration to island B both perform a decrease. Therefore, with regard inequality, island B as a lower rate and island A has a higher rate when compared to part I.

Adding the non-tradable good improves the previous model by imposing stricter conditions for equilibrium. This suggests that in the islands with higher technology, the non-tradable goods have higher price even though these goods are the same for all islands. The intuition is that higher technology islands have higher wage for the tradable goods. To ensure that people willing to work for the non-tradable sector, two sectors must have the same wage. To cover the additional cost from the wage, the non-tradable sectors must increase the price. This is the Balassa–Samuelson effect (Samuelson, 1964 ) and Kravis and Lipsey ( 1983 ), which is found statistically significant by Samuelson ( 1994 ). Vaona ( 2011 ) and Nenna ( 2001 ) provide evidence supporting it from intra-country level in Italy, and Songtao ( 2009 ) tests it for real estate’s price between cities in China, indicating that the cities’ higher technology level is positively correlated with the wage and price of real estate sector, which is the rationale of applying Balassa–Samuelson effect on the city-level.

The adjusted model used in this section leads to a similar distribution when contrasted with that of part I. However, the non-tradable goods provide another intuition to explain labour mobility and its causes. The labours also consider the price of non-tradable goods as a factor determining the decisions of labour mobility. When considering where to work, people do not only consider the wage but also the purchase power of it on local food, service, or accommodation. For the labours with higher talent but lower wealth, they mainly rely on wage income. As we discussed in the Appendix 2 , the wage in large cities is more affordable for non-tradable goods. Comparing to proposition 1 of part 2, they are more likely to move to the cities with higher technology. Conversely, for labours with lower talent but higher wealth who mainly rely on capital income, they are more likely to move to the cities with better environment because the price level is higher in large cities. For people with low talent and low wealth or high talent and high wealth, the conclusion of proposition 2 of part 2 is the similar as they also balance between the gain of more affordable wage income and less affordable capital income from moving to a higher technology city.

It also accounts for the low wage-price ratio in cities with superior environments. This is consistent with the positive correlation between the natural environment and house prices in previous literature. Luttik ( 2000 ) and Donovan et al. ( 2019 ) estimate the effect of demographic factors on house prices and reveal the significant positive correlation between trees, water, open spaces, and house prices. Furthermore, Catte et al. ( 2004 ) and Steegmans and Hassink ( 2017 ) find that wealth of the buyers has a significantly positive effect on housing prices. Generally, housing prices are also positively correlated to the level of local wages. However, there are also cities with superior environment where local wages are relatively low also with high housing prices. Therefore, we might assume that areas with higher house prices are more likely to be those with higher-income residents whose wealth drives up house prices. This implies that cities with relatively low technology but a relatively high quality of environment might also attract households with high incomes. Achieving a high income in the city with low wages is brought about through these households that have capital income from other cities. This implies that if a city government spends too much on developing tourism while ignoring the investment on R&D, the population in that city will be people with high capital store and low skill, which drive up the price level but do not help with the wage increase. A typical city in China is Sanya, which is famous for its natural environment. Its house price-wage ratio is of top 5 in China while its average wage is even not in top 50 (Chinese National Bureau of Statistic, 2022 ).

Empirical analysis

We apply the empirical analysis to support the Lucas-Prescott style island model. The empirical analysis is based on the American population movement data in IPUMS USA from 2016–2021 at state level. And we use the patent data from US patent and trademark office to proxy for the technology level, and the higher number of patents indicates the high level of state technology level. The air quality index (AQI), the comprehensive evaluation of pollutants such as SO2, NO2, PM10, PM2.5, O3 and CO, from US Environmental Protection Agency to measure the environmental level. While, the bigger AQI implies the worse state environment.

To test the impact of individual wealth and education on the living choice, we construct the following Logit model:

and Probit regression model:

where i represents citizen, j represents state and t represents year. Environmental takes value of 1 if individual i lives in a state j with good environment quality and 0 otherwise, by the median of AQI. And Tech nology takes value of 1 if individual i lives in a state j with high technology and 0 otherwise, by the median of patent number. Φ is the cumulative distribution function of the standard normal distribution. Education level (Education) is the proxy variable for individual skill, measured as the sequence from 1 to 11 representing the lowest education level to the highest level and the value of home with logarithm is used to proxy for individual wealth. Controls is a vector of individual control variables include sex, age, logarithm of one plus income (including rental income from housing) and owning farm or not. And the descriptive statistics of all variables are reported in Appendix 3 . To control unobservable factors potentially affecting living choice, we further control the year, work industry and county fixed effects, with standard error clustered at family level.

Following Taiwo ( 2013 ), the results are presented Table 1 , with Columns (1)–(4) reporting Logit model and Columns (5)–(8) reporting Probit model. And columns (1), (3), (5) and (7) report the result of odds ratio, with others reporting the coefficients. The Columns (1)-(2) and (5)-(6) show that the probability of citizens living in states with poor environment increases with their skill level and decreases with their wealth. And Columns (3)-(4) and (7)-(8) reveal that those owning little wealth with high skill level have higher chance to live in state with relatively high technology level. In conclusion, citizens with high skill-level and little wealth tend to choose the state with poor environment and high technology level, and these with low skill-level and huge wealth prefer to live in state with good environment and low technology level. This is consistent with the pervious theoretical analysis that, as higher technology of the location and education level of the individual bring higher wage level, those with little endowment wealth but higher education level have to work in places with higher technology but worse environment to enjoy higher wage to cover their expense. On the contrast, labours with higher wealth tend to live in a place with better environment as they can benefit from capital rent wherever they live and they can gain more utility from the environment. However, we only regress the labour choice at the state level. The further research will be conducted to test if the theory still holds at the county/city level, which is more precise and convincible.

This paper describes and derives a Lucas-Prescott style island model, to study the choices of heterogeneous agents’ decision about where they want to live. Differing from other islands model which assume the implementation of the stochastic technology process, it utilises endogenous technology growth, which in turn influences personal human capital growth. This leads to the balanced growth equilibrium in steady state, which is potentially the first model that combines balanced growth and the Lucas-Prescott model. Compared to the conventional Lucas-Prescott models where only the distribution is fixed in steady state, this model provides the fixed location of each agent, which admittedly makes it less flexible. However, that is compensated by less restrictive steady state conditions, which leads to multiple steady states.

The baseline model’s steady state indicates that the islands (cities) where people ideally want to stay in must be the islands on the frontiers (see Fig. 2 ). Among these islands, agents that have a higher speed of learning and lower capital tend to reside in urban metropolitans, while people who rely mainly on non-wage-based income prefer to live in a city with better environment. It leads to the U-shape curve of the wage income inequality in terms of the technology of these islands, which is consistent with Nord’s ( 1980 ) research. However, in terms of total income, the inequality is ambiguous. The two-goods model includes both tradable and non-tradable goods, which interprets the high price-wage ratio of the cities with good environments through the Balassa–Samuelson effect. Even though the implications behind the choice of a location still holds, its magnitude is increased by the impact the price of non-tradable goods.

However, this paper does not consider the role of the government to allocate resources to attract workers, support technology development, and improve the environment. It also lacks the deep analysis of the real-world data. To complete the research, the future study will add the government to the model and suggest different policies for the government with different goals. Then we will simulate the model, which is calibrated based on the data of US. Also, we will evaluate the model based on microdata of individual labour at the county/city level. For example, apart from the labour choice, which is mentioned before, macro-level data of each city’s price level will be regressed to examine the fit of the simultaneous effects of migration and the price of non-tradable goods on each other to the model.

Data availability

The data generated during and/or analysed during the current study are available in the supplementary files.

The level of urbanization is calculated as the proportion of citizens in the urban area to the total population within the country. The data is accessible from World Bank database at: https://data.worldbank.org/indicator/SP.URB.TOTL.IN.ZS

The data is accessible from World Bank database at: https://data.worldbank.org/indicator/EN.URB.LCTY.UR.ZS

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Qi, T., Gao, Y. & Huang, Y. A Lucas island model to analyse labour movement choice between cities based on personal characteristics. Humanit Soc Sci Commun 11 , 1138 (2024). https://doi.org/10.1057/s41599-024-03627-9

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Research Article

What is a heat wave: A survey and literature synthesis of heat wave definitions across the United States

Roles Conceptualization, Data curation, Funding acquisition, Methodology, Project administration, Validation, Writing – original draft

* E-mail: [email protected]

Affiliations Department of Geography, Environment, and Spatial Sciences, Michigan State University, East Lansing, Michigan, United States of America, Remote Sensing and GIS Research and Outreach Services, Michigan State University, East Lansing, Michigan, United States of America

Roles Formal analysis, Visualization, Writing – review & editing

Roles Funding acquisition, Methodology, Writing – review & editing

Affiliation Department of Geography, University of Florida, Gainesville, Florida, United States of America

• Erin L. Bunting, 
• Vasily Tolmanov, 
• David Keellings

• Published: September 5, 2024
• https://doi.org/10.1371/journal.pclm.0000468
• Peer Review
• Reader Comments

Heat waves are the last extreme weather events without a formal, on the books, definition. Instead, across the U.S. those working on extreme heat event management, forecasting, and planning are using differing definitions in their work. With such differing definitions being used there are widespread impacts including some to human and environmental health, natural resource management, and long-term emergency management planning. For instance, when should heat advisories for vulnerable populations be released when an event impacts a region using multiple definitions? There are concrete and justifiable reasons for the lack of a formal heat wave definition including, at its simplest, differences in what temperature is extreme enough, compared to the region’s climatological regimens, to be deemed as an extreme heat event or heat wave. This study looks for patterns and commonalities in emergency managers and climatologists, those most commonly addressing or planning for such events, definition of heat wave events through a review of the literature and widespread survey across the United States. Through a short 11-questions survey and subsequent text mining, we find widespread variability in the common heat wave definitions but a consistent pattern of core key term usage including aspects of heat duration, extreme temperature, and humidity. However, we also see little to no usage of non-climatological variables such as exposure, vulnerability, population, and land cover/land use.

Citation: Bunting EL, Tolmanov V, Keellings D (2024) What is a heat wave: A survey and literature synthesis of heat wave definitions across the United States. PLOS Clim 3(9): e0000468. https://doi.org/10.1371/journal.pclm.0000468

Editor: Teodoro Georgiadis, Institute for BioEconomy CNR, ITALY

Received: December 14, 2023; Accepted: July 13, 2024; Published: September 5, 2024

Copyright: © 2024 Bunting et al. This is an open access article distributed under the terms of the Creative Commons Attribution License , which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

Data Availability: All data needed to recreate this article is provided in the supplemental materials associated with the article. Identifying data will not be released including the survey takers names or contact information, but these data are not essential for study recreation. This project was deemed exempt from full IRB review. Any questions related to the data, or the article can be addressed by emailing the authors Erin Bunting ( [email protected] ) or David Keellings ( [email protected] ). If you have any data requests or additional questions, and the authors are not available, please feel free to contact MSU RS&GIS ( [email protected] ). This group has prior knowledge of the project and a copy of project and IRB documents on a secure server. If you have any questions or concerns regarding the survey, contact please contact the Michigan State University Human Research Protection Program (HRPP) office at 517-355-2180 or via email at [email protected] . Please use the following MSU Study ID: STUDY00004016 if you communicate with MSU HRPP.

Funding: This research was funded by a grant from the National Science Foundation GSS program (Award #2203235). Multiple people and organizations made this publication possible and the authors wish to express their gratitude, especially to Dr. Laura Myers and Jacob Reed at the University of Alabama, Dan Wanyama, and the Staff of Remote Sensing and GIS Research and Outreach Services (RS&GIS) at Michigan State University. Additionally, we thank the reviewers for their time and effort put into manuscript review.

Competing interests: The authors have declared that no competing interests exist.

1. Introduction

Extreme weather and climate events have been impacting human and natural landscape since the beginning of time. However, with changing climate patterns we are seeing greater impacts of these events globally. As stated in the most recent IPCC report it is an “established fact” that human induced change has resulted in “an increased frequency and intensity of some weather and climate extremes since pre-industrial times” [ 1 ]. With such changing patterns it is important to look at not just the impacts and patterns of such events but the premise of the event definition itself. Extreme weather and climate events are broadly defined as severe weather or climate conditions that induce devastating impacts to the human and natural landscapes. While such events can be weather-related (short in duration), or climate related (long in duration) there is a basic understanding that the event is defined as atypical and beyond the normal. Almost all these extreme events (e.g., hurricanes, tornadoes, blizzards) have standard definitions related to what triggers the event, how they are measured, and their severity classification. For instance, with hurricanes, the Saffir Simpson class is used to define the pressure and wind speeds associated [ 2 ]. With tornadoes, the Enhanced Fujita Scale (EF) uses derived engineering wind estimates in assessing strength and resulting damage [ 3 ].

While almost all climatological events have standard definitions one of the deadliest does not, heat waves. Over the past decade, heat waves of varying durations and intensities have impacted much of the globe. For instance, the 1995 heat wave in the central United States resulted in more than 1000 deaths [ 4 , 5 ]. Further, across France, the large 2003 European heat wave resulted in excess mortality of approximately 15,000 individuals, up 60% from normal mortality patterns [ 6 , 7 ]. In line with the IPCC remarks on trends of extreme events there has been an increased frequency of heat waves not just across the US and France, but across Europe, China, Australia as well [ 1 ]. Additionally, it has been projected that heat waves will be more frequent, intense, and longer-lasting into the future [ 1 , 8 – 10 ], thus raising concerns on planning for such events.

There is no worldwide consensus on a heat wave definition though its usually thought simply as an extended period of extreme heat. Not grounded in academic or climatological literature, the Merriam dictionary defines heat waves as “a period of unusually hot weather”. Additionally, in many published articles, simple definitions based purely on temperature are utilized, including those as simple as “an extreme heat event is defined when the temperature exceeds a given threshold with an appropriate spatial extent” [ 11 ]. Attempts have been made at standardizing a heat wave definition. For instance, in 1996 Environment Canada provided a more scientifically grounded definition of a heat wave as a period of more than three consecutive days of maximum temperatures at or above 32 degrees Celsius [ 12 ]. Additionally, governmental groups both in the US and around the world have developed de facto definitions of heat waves including: the US National Weather Service, NOAA, and UK Met Office. These definitions are being developed for the issuance of heat watches and warnings and therefore should be pertinent for use by emergency managers and state climatologists. With this in mind, one would expect high overlap between national government definitions of heat wave and those from managers and state climatologists. The aforementioned governmental groups define heat waves as such:

• US National Weather Service : A period of abnormally hot weather generally lasting more than 2 days. Heat waves can occur with or without high humidity.
• NOAA : A period of abnormally and uncomfortably hot and unusually humid weather. Typically, a heat wave lasts two or more days.
• UK Met Office : An extended period of hot weather relative to the expected conditions of the areas at that time of year, which may be accompanied by high humidity.
• World Meteorological Organization (WMO) : A period where local excess heat accumulates over a sequence of unusually hot days and nights.

What is lacking from these definitions is consistency regarding temperature thresholds, metrics, durations, or number of days used to define such events [ 13 ]. Further, even using these definitions, adverse heat impacts on human health have been documented at lesser extreme temperatures and durations [ 12 , 14 , 15 ]. It’s important to note that the use of various heat wave definitions results in temporal variability in heat wave classification, inability to compare events and synthesize results across regions, and inconsistent terminology in the literature. Many of these challenges can be overcome by finding some consistency across regions and definitions.

Why it is difficult to develop a consistent heat wave definition is fairly obvious, heat waves differ in their intensity (magnitude), extent, duration, and scope of impact [ 16 ]. Numerous studies have used different thresholds of mean or maximum temperature [ 17 ], percentiles of maximum temperature, heat indices, or even combinations of thresholds [ 18 , 19 ]. The common variables of these studies being the use of intensity and duration factors. [ 20 ] looked at 45 definitions of heat waves, combining 5 temperature thresholds, three temperature indicators (daily mean temperature, minimum temperature, and maximum temperature), 5 percentile metrics (90 th , 92.5 th , 95 th , 97.5 th , and 99 th ), and multiple event duration lengths (2, 3, and 4 days) to assess how different definitions align with mortality patterns. Overall, [ 20 ] found the best model fit, and therefore best heat wave definition, using daily mean temperature in the 99 th percentile in combination with a 3-day event duration. Similarly, two studies, one in the US and another from West Africa, found the best fit model was produced by a heat wave definition using both minimum and maximum temperatures in the 90 th percentiles with an event duration of 3 days [ 21 ]. Drawing from these, and other, studies we can see a heat wave definition needs to include factors of: (1) intensity or magnitude: based on a tested index or temperature threshold, (2) duration: defining the persistent of an event to be a heat wave, (3) extent: geographic areas impacted and measures of exposure, and possibly (4) severity [ 22 ].

There are no doubt other factors contributing to heat wave impacts such as frequency, timing, event size, and population density. Incorporation of these factors into a unifying heat wave definition is fraught with complications. For instance, a higher frequency of hot and humid conditions do not necessarily result in a heat wave and severe heat wave impacts [ 12 ]. Similarly, regions experiencing more hot and humid summer conditions already have physiological, behavioral, and infrastructure adaptations to extreme heat, likely reducing the harmful effects [ 12 ]. However, with such heat wave components (intensity, duration, and extent), we can begin to understand the social, cultural, and physical impacts of extreme heat events. For instance, with such a holistic definition we can begin to develop temporary modification to lifestyles to minimize heat stress exposure and impacts. More clearly such a definition enables evasive action and management practice to be developed.

Heat waves can be defined in several ways, through absolute and relative approaches. With an absolute heat wave definition an exact event duration threshold would be set in tandem with a pre-determined temperature and/or heat stress index level [ 12 ]. Whereas, if a relative heat wave definition were developed it would have to take into consideration acclimatization to weather, exposure, and human dimensions in addition to region specific climate trends. Most published studies on heat wave definitions look to model or develop the core metrics, threshold, and durations to define event occurrence. In this study we ask those on the ground for insight into heat wave event definition. Through a simple survey conducted across the United States in 2020 we look at what definitions each respondent is currently using, what variables they see as critical, impacts of differing definitions, and how relative definition approaches are used in their work. Overall, it was hypothesized that (1) emergency managers would have a different perspective on heat wave definition, especially as it relates to human exposure and acclimatation, (2) differing local to regional climate trends across the country would result in different definitions north to south across the U.S., and (3) only atmospheric variables would be considered in respondents’ heat wave definitions.

2. Data and methods

2.a. survey development.

The survey was designed to see how those involved in heat wave forecasting and management define such events and what factors contribute to their definition. The 11-question survey also included space for respondents to provide additional text and information to clarify their definitions and provide other important details. The survey was developed, tested, and IRB approved at Michigan State University and the University of Alabama. Respondents, none of whom were minors, were informed of survey privacy and provided consent language prior to taken the survey. All respondents provided written consent at the onset of the survey. The survey was developed within Qualtrics and consisted of 11 questions ( Fig 1 ).

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https://doi.org/10.1371/journal.pclm.0000468.g001

The survey commences with questions of occupation, geographic extent of work, and zip code of residence ( Fig 1 ). Question 4–11 are, using free response, asking how, in their professional capacity they, define heat wave events. Additionally, we ask: what variables are associated with the definition (in case this is not mentioned in the free response), what non-atmospheric variables are included, and looks to understand how event duration, size, and time of year factor into their definition.

The survey was open for approximately five months. Distribution of the survey occurred through emails to: (1) state climatologists listserv, (2) emergency management associations, (3) a contact list for all state-recognized emergency managers, and (4) the American Meteorological Association listserv. Overall, the survey was disseminated through associations and email groups related to the parties of interest.

2.b. Data processing and analysis

Once the survey period was completed the Qualtrics survey was closed, and the data were downloaded locally. To clean the data, we first looked at the completeness of responses. Overall, 137 individuals fully completed the survey and 25 partially completed the survey. It was decided if a respondent answered at least half of questions 4–11 (see Fig 1 ) that these would still be included in the analysis. Other responses were removed from the analysis.

Data analysis occurred in several ways. Text mining and pattern analysis were conducted within R [ 23 ]. Initially, analysis began with simple frequency counts of factors such as geographic extent of work, field of work, etc. Next, for questions four and five, text mining was conducted using several R packages including SnowballC [ 24 ]. First, by question, the responses were merged into a corporal collection of phrases containing natural text. From there the tm_map function was used to remove symbols, number, punctuation, and common words (i.e., cause, the, and, is, have, are, was, be, of) from each survey response entry. The resulting text is not in sentence format but rather the key words within each response.

After the data were cleaned for text mining, analysis began with simple frequency counts. Using this simple statistic, the common terms or words utilized by the respondents were tallied by question. Terms or words used more than twice were preserved in the analysis. In addition to the frequency analysis, word clouds were constructed using the wordcloud package in R [ 14 ].

The word cloud represents the extremes of thought, terminology, and definition of heat waves. The word clouds also highlight the frequency in term utilization by the respondents. For the remaining questions simple summary statistics were completed in R.

3.a. Profile of survey respondents

We see large diversity in the response pool, both spatially and across profession. Overall,162 individuals took part in this project with 137 fully completing the survey. This corresponds to an 84.55% completion rate. The 162 responses came from across the US and across a wide variety of subfields related to climatology, emergency management, and meteorology. Spatially, responses were collected from 43 of the 50 states with Hawaii, South Carolina, Massachusetts, Rhode Islands, Connecticut, Virginia, and West Virginia being the exceptions. While there are no direct responses from those states, they are partially represented by those that work regionally, nationally, or at the global scale. While there are survey responses across the country there is a slight skew to the southern portion of the United States. For those respondents that work county to statewide we see the most responses from Alabama, Mississippi, Florida, Arizona, and Texas ( Fig 2 ). However, there are responses at this scale spread evenly across the U.S.

Dots represents those that work at the county level. Colored polygons represent those that work at the state level and the number of people that responded to the survey that work at the state level. Numbers represent those that responded that worked at another scale of geometry (e.g., city, community, multiple counties, townships, etc.). Not represented are those that worked globally (n = 8), nationwide (n = 4), and those that work sub-county level (city or community). Map created in ArcGIS using survey data and a states shapefile from the US Census Bureau ( https://www.census.gov/geographies/mapping-files/time-series/geo/carto-boundary-file.html ).

https://doi.org/10.1371/journal.pclm.0000468.g002

The professional profile of those that completed the survey is diverse and does not skew to one group of individuals or those with certain specialties. Eighty-seven (53.7%) of the completed surveys came from those that identified forecasting as their occupation. Of those 62 worked across multiple counties in a single state, 11 at the state level, 7 at the regional (multiple states or parts of multiple states), 3 at the county level, 2 at an “other level” (city to local level), 1 globally, and 1 at the community level. After forecasting the next highest group of responses came from emergency managers. Overall, 46 (28.2%) emergency managers from across the US completed the survey. Of those emergency managers 32 worked at the county level, 2 worked across multiple counties, 1 worked at the regional scale (across multiple states), 1 worked at the national level, 1 worked at the community level, and the remaining 9 worked at other scales (e.g., tribal lands, city, ecoregion, etc.). Lastly, 29 individuals identified their career as “other”, including: researchers, retired state climatologists, climatologists, land managers, and those in academia. From this group the majority worked at the state to global scale.

3.b Defining heat waves

Text mining of survey responses showed interesting keyword usage patterns ( Fig 3 ). For the question “What is your definition of the climatological term ‘heat wave’”, heat was not the most used word, instead days was mentioned 71 times by respondents. Answers related to this term included definitions like: “Several days of 95+ degrees”, “A period of multiple days beyond normal temperatures”, and “At least 3 consecutive days of high maximum temperatures”. After days, the terms heat (n = 68), period (n = 65), normal (n = 47), and high (n = 42) were the other common terms ( Fig 3 ). Overall, this word usage pattern highlights a highly important and common thought pattern in defining heat waves, such extreme events have a duration aspect that needs to be considered and defined. Heat waves are multi-day extreme events.

Response trend word clouds and frequency counts for the questions: (A) “What is your definition of the climatological term heat wave?”, and (B) “What atmospheric variables are part of your definition of a heat wave?”, and (C) “What other atmospheric variables are part of your definition of a heat wave”.

https://doi.org/10.1371/journal.pclm.0000468.g003

When asked, “What atmospheric variables are part of your definition of a heat wave”, the most selected term was maximum temperature (n = 129) followed by heat index (n = 85), minimum temperature (n = 75), and humidity (n = 74). These four terms were far more common than the next terms of the list, average temperature (n = 45) and other (n = 25). Respondents were given a list of possible terms for this question and asked to select all that apply to their definition of heat waves. The terms included include maximum temperature, minimum temperature, average temperature, humidity, heat index, and other. This word usage pattern highlights that extreme terms are central to the definition of heat waves.

Lastly, respondents were asked “What other atmospheric variables are part of your definition of a heat wave?” This question was asked so respondents have free response, instead of choosing from a bank of options as with the previous questions, the climatological variables that they use in management, forecasting, and planning. It is important to note most respondents did not list any additional atmospheric variables as part of their heat wave temperature. Of those that did the most common response was wet bulb globe temperature (WBGT), wind, cloud cover, and insolation. A few respondents listed, repetitively, humidity and heat index, in response to this question. Overall, this word usage pattern highlights the strong pattern of traditional climatological variables in the definition of heat waves, rather than characteristics of land, demographics, human health, or exposure.

3.c Beyond climatological terms, other factors to considered in defining heat waves

Beyond traditional climatological terms we asked respondent “Does your definition of a heat wave include non-atmospheric variables?” Only 27.5% of respondents replied in the affirmative that they did include non-atmospheric variables in their definition of a heatwave ( Fig 4 ). The common non-atmospheric variables included in the heat wave definition were grouped into categories of: (1) impact on humans, (2) seasonal variation, (3) physical variables, and (4) other. The highest percentage of responses were within the impact to humans categories with 35.3%. Common non-atmospheric variables listed by respondents included: soil moisture, land type, duration, percent impervious surfaces, and crop stress. Most respondents that included non-atmospheric variables in their definition of heat waves were forecasters (n = 25), with only 5 emergency managers and those identified as “other” in their career including non-atmospheric variables. Geographically, those that included non-atmospheric variables mostly worked at the state to multi county scale (n = 22). Others that included non-atmospheric variables worked at varying geographic extents including county scale (n = 7), regional scale (n = 3), and global scale (n = 2). Spatially, that 27.5%, where not clusters in one portion of the US. Those that included non-atmospheric variables spanned from Arizona to Vermont.

Response trends to the questions: (A) “Does your definition of a heat wave include non-atmospheric variables?” and (B) “If yes, what other variables do you include?”.

https://doi.org/10.1371/journal.pclm.0000468.g004

Next, respondents were asked if their heat wave definition included a threshold that must be surpassed to be considered a heat wave and what threshold measurement they used. More than 56% of respondents said yes, their definition included a threshold that must be crossed. Of these 18 were emergency managers, 33 were forecasters, and 16 listed other as their career. As such, of the respondents that completed the survey approximately 38% of forecasters, 39% of emergency managers, and 55% of others included a threshold in their heat wave definition. Spatially, those that included a threshold worked across all geographic extents from community / local to global, though slightly more worked at the statewide or multicounty scale.

It was thought that the main threshold both emergency managers and forecasters would use in their definition would be related to temperature. Many of the provided definitions stated something like:

“Temperature above 95 degrees Fahrenheit for an extended period of time”

“A persistent anomaly in daily surface temperature usually many days about the 98 th percentile.”

Instead, survey results show that only 45.7% of respondents reported using temperature thresholds in their heat wave definitions, followed by heat index (27.9%), heat duration (23.5%), and heat risk ( Fig 5 ). Spatially, if we look at the common temperature threshold mentioned by survey respondents there is an interesting dynamic playing out ( Table 1 ). Those surveyed from the Northeast, Southwest, and Central regions of the United States, as defined by the NOAA climate regions, all listed a temperature threshold of 90°F with little variability. The lowest temperature threshold mentioned was 80°F and it was from a respondent in the south region. Whereas the highest threshold reported was 105°F, occurring in both the East North Central and South regions. Overall, a north to south temperature threshold gradient was expected, as the more southerly regions are subject to climatically higher mean temperatures, but this was not seen in the survey responses.

Response trends to the questions: (A)” Does your definition of a heat wave include a threshold that must be crossed in order to be considered a heat wave?”, and (B) “what is the threshold measurement that you use?”.

https://doi.org/10.1371/journal.pclm.0000468.g005

https://doi.org/10.1371/journal.pclm.0000468.t001

Fig 5B shows that numerous respondents suggest a threshold in their heat wave definition based on duration. During the survey respondents were specifically asked “Does your definition of a heat wave include a minimum duration”. This question was asked, in tandem with the aforementioned in case a respondent did not feel duration was a threshold measure. Over 74% of respondents said yes that event duration was a part of their heat wave definition. Of these 25 were emergency managers (54.3% of EM total population), 56 where forecasters (64.4% of F total population, and 19 listed their career as other. Importantly, the most noted durations for events were 2 and 3 days ( Fig 6 ). Overall, 22.2% or respondents mentioned 2 days as the minimum duration for a heat wave to be defined and 56.6% listed 3 days as the minimum duration. The response pattern of did not vary by geographic extent of work or the region respondents work in.

Response trends to the questions: (A) “Does your definition of a heat wave include a minimum duration?”, and (B)” If yes, how many days?”.

https://doi.org/10.1371/journal.pclm.0000468.g006

At this point, respondents had solely been asked about common aspects of heat wave definitions such as duration, intensity, etc. The next question of the survey asked, “Is size of area affected part of your definition of a heat wave?” Only 21.8% of respondents considered event size in their heat wave definition, equating to just 29 respondents. Of these there was an even split between emergency managers and forecasters, the geographic extent of their work was mostly single or multiple counties, and almost all included duration in their heat wave definition.

The majority of those that responded in the affirmative said that a heat wave had to have a duration of 2 or 3 days to be defined as such an event. The range of durations suggested by those surveyed was as short as 1 day (3 respondents) and as long as 10 days (1 respondent) ( Fig 7 ).

Response trends to the questions: (A) “Is size of area affected part of your definition of a heat wave?”, and (B) “If yes, how is size incorporated into your definition of a heatwave?”.

https://doi.org/10.1371/journal.pclm.0000468.g007

If a heat wave only impacts a small area, does it matter in emergency management and forecasting as much as large events? That question was the impetus for the next survey question, “is size of area affected part of your definition of a heat wave.” The vast majority (78.2%) of people said no, size does not matter. Those that answered yes to this question were almost all forecasters (except 2 out of 14). Those that answered in the affirmative had a clear theme, larger events impact more people compared to isolated events and that is why event size matters. With this theme several people mentioned that an event needs to be state-wide or span multiple counties (44.8% of the previous questions affirmative answers).

The last two questions of the survey look to see how respondents think about defining heat waves across space and time. Respondents were asked “Is your definition of a heat wave dependent on time of year?” This question was almost a 50/50 split in terms of percentages with 53% saying the definition is not time of year dependent and 47% saying it is ( Fig 8 ). For those that answered in the affirmative they were asked how their definition varies through the year. There were a wide range of responses to this follow up question from those mentioning seasonal threshold values to others saying only summer matters as it’s the warmest season. Overall, the consensus of those surveyed is well represented by one respondent’s remakes, “I generally only call things "heat waves" when it is “hot” outside. I wouldn’t call a winter stretch of warmer than normal weather a "heat wave" unless it was drastically warmer than normal.” There is a consistent trend in these types of answers with others saying outright “heat waves have only occurred climatologically in our late spring to early fall months, when it’s hottest”. However, there were a small group (labeled statistical in Fig 8 ) that again link back to thresholds and say, in their opinion, that heat waves can happen if the temperatures exceed the 95 th percentile for that given time frames normal.

Response trends to the questions: (A)” Is your definition of a heat wave dependent on time of year?”, and (B) “If yes, what time of year?”.

https://doi.org/10.1371/journal.pclm.0000468.g008

Lastly, respondents were asked if their definition of a heat wave varies across space. This question was asked to see if one core definition of heat waves cannot be developed and instead a regional definition would be needed. Overall, only 36.3% responded in the affirmative whereas 63.7% said their heat wave definition did not vary across space ( Fig 9 ). Those answering in the affirmative, that their definition varied across space, were then asked how with the options of: (A) regional differences, (B) type of territory, (C) statistically, (D) varies by the gridded data, and (E) other. Overall, 42.9% of respondents that thought heat wave definitions should vary across space thought there were regional differences. When asked to explain their answer respondents had a variety of answers and mentioned topic such as: “definitions can be different across climate regions because citizens are acclimated to different levels” and “In my work the western high plains should have a higher threshold for defining heat waves than the eastern portion of the Southern Plains”, and “Since humans can become acclimated to "normal" conditions, I would vary the definition based upon a certain amount above climatology”. Next, 22.5% of respondent said heat wave definitions should vary because of type of territory. Those that responded in this manner mentioned: “amount of vegetation vs bare ground is important” and “population density and impervious surfaces need to be considered to account for urban heat island effects”. Third, 22.5% said statistically heat wave definitions should vary spatially. These respondents provided further understanding of their response with comments such as: “Heat wave might be the top 0.1% of high temperatures of all time for each location” and “temperature percentile varies by location”. Lastly, only 6.1% of respondents said their definition varies over space because of gridded data. Specifically, those that answered in this manner added comments like: “heat risk is calculated on a spatial grid by entire forecast area” and “gridded temperature data is 2.5 km resolution—so the values for defining the heat wave vary spatially even if the definition remains the same.” Overall, these responses highlight a need to better understand duration, thresholds, and the underlaying population exposure.

Response trends to the questions: (A) “Does your definition of a heat wave vary across space?”, and (B) “How does it vary spatially?”.

https://doi.org/10.1371/journal.pclm.0000468.g009

4. Discussion and conclusions

Heat waves are regarded by the U.S. National Weather Service as a major, in fact leading, cause of weather-related fatalities in the U.S. in most years [ 18 ]. Closing the gap on a formal heat wave definition is important because of such direct affect that these extreme events can induce. A formal definition is important to multiple subfields, beyond emergency management and forecasting, as in the literature it has been consistently noted that the direct adverse effects of heat waves include (1) increased demands for water and electricity [ 25 – 28 ], (2) reduced productivity and overall labor efficiency [ 25 ], (3) drought and overall crop stress or failure, and (4) human health, including cardiovascular and respiratory damage in addition to death. Further, in the literature heat-related studies have been published related to land management, policy development, vulnerability/exposure regarding human health, urban development, emergency planning, and ecosystem health.

Overall, our population is vulnerable to heat waves and therefore we need a better understanding of these extreme events. For instance, the impacts of heat waves on human health are widely documented regarding mortality and morbidity [ 29 , 30 ]. That said, heat wave vulnerability is unequal and unevenly distributed across both human and natural landscapes. The elderly, those residing in nursing homes, and the chronically ill are readily identifiable as susceptible subgroups, high at risk for extreme heat impacts, and studies have criticized the lack of effective heat management for such populations [ 31 – 35 ]. These populations are not the only ones impacted by heat waves and the way such events are managed. Children have a higher sensitivity, outdoor workers have more extensive exposure, and the homeless are just a few of the other vulnerable populations [ 36 – 40 ].

Heat related deaths occur when a rapid temperature increase outpaces the body’s ability to cool itself, though perspiration and increased blood circulation [ 41 ]. There are compounding factors to such mortality risk including high humidity and overall exposure. If we examine the characteristics of heat waves mentioned throughout this study and our survey (duration, intensity, timing, size) its known that these factors negatively impact public health by increasing the risk of heat-related mortality [ 41 ]. For instance, long duration heat events increase exposures, elevate even the daily minimum temperature, and limit the body’s ability to recover [ 17 , 27 ]. Additionally, large-scale events are more likely to expose broader human populations to such extremes, increasing the population vulnerable to such an event. Lastly, the timing of an event can have multiple implications including (1) early extreme events can result in large populations of people unprepared and (2) events during peak summer months can be assumed to be more intense in nature. Beyond health impacts, the timing of such events can alter soil available moisture, impacting plant phenology and productivity. With such changes in soil moisture there are not only connections to widespread drought but also to impacts of cropping and overall harvest quality and quantity, again linking back to human impacts. Overall, in the US, the Center for Disease Control (CDC) estimates that heat related deaths average over 1000 per year [ 42 ]. However, the impacts of extreme heat stretch far beyond the health ramifications and therefore needs to be studied and defined more holistically.

How can a formal unified heat wave definition impact emergency management? Simply, with the development of a formal definition and associated research emergency managers and forecasters can know what to expect, outcome wise and in knowing the vulnerable populations, and plan for during extreme heat events. Much research has gone into analyzing heat wave definitions to see how they align with differing outcome patterns, particularly human health impacts. For instance, Knowlton et al, analyzed heat wave induced hospitalizations and emergency room visits resulting from the 2006 California extreme event and found that a definition based on a higher maximum temperature threshold was associated with a greater relative risk for hospital admission [ 43 , 44 ]. Other studies have tested heat wave definition to decide the ideal scenario for the opening of cooling centers and to consider moving vulnerable people to safer locations [ 45 , 46 ]. Beyond hospitalization and evacuation with a formal heat wave definition managers can understand, through research of trends, what to expect for certain mortality risks. For example, Dong et al. 2016 found that a heat wave definition using the 93 rd percentile of maximum temperature and 5 day event duration was the best way to understand the trends between extreme heat and cardiovascular mortality [ 47 ]. These examples, explicitly related to health outcomes and exposure due to extreme heat are just a few ways in which emergency management could use such information and data.

We live in a warming climate, and with such changing regimes it’s projected that the duration, intensity, and frequency of heat waves will increase [ 48 ]. From the literature and survey, we can surmise a few key aspects of a formal heat wave definition. Factors that need to be considered in the formal definition include duration, intensity (a climatological threshold), and exposure. Survey results show that the majority respondents report a heat wave can be defined as an event that lasts at least 3 days. The mean duration listed by survey respondents was 3.14, the mode was 3 days, and the median was 3 days as well. Overall, the durations listed by respondents ranged from 1–10 days. Regardless of occupation and geographic extent of work most respondents felt a threshold value needed to be crossed for a heat wave to formally be defined. Both percentiles and numeric thresholds were suggested. Additionally, a large group of respondents felt that maximum temperature was the key metric to develop such a threshold. For those that wanted to include percentiles in their heat wave definition the 95 th percentile was the most noted. In terms of absolute temperatures there was a large range of possible thresholds suggested, 90–105 degrees. The mean temperature threshold suggested by respondents was 94.6 degrees. Interestingly, there were no survey response trends suggesting for spatial variation in heat wave definitions. In terms of time of year, most felt that heat waves would only be defined in the hottest months and are not solely associated with any monthly or seasonal temperatures beyond the normal. One of the most important non-climatological aspects brought up by survey respondents was exposure and associated population density. Such survey results do not solidify a formal heat wave definition, but they do show extremely similar thought processes across different occupations and regions of the US. With such similarities in defining heat waves there is no doubt similar patterns of use for such data in emergency management and forecasting, and perhaps for a future unified definition of heat waves.

Supporting information

S1 data. deidentified survey data collected including the full irb information and question in the header of the data file..

https://doi.org/10.1371/journal.pclm.0000468.s001

Acknowledgments

Multiple people and organizations made this publication possible, and the authors wish to express their gratitude. The authors wish to especially thank Dr. Laura Myers and Jacob Reed at the University of Alabama, Dan Wanyama, and the staff of Remote Sensing and GIS Research and Outreach Services (RS&GIS) at Michigan State University. Additionally, we thank the reviewers for their time and effort put into manuscript review.

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