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15 Literature Review Examples

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Dr. Chris Drew is the founder of the Helpful Professor. He holds a PhD in education and has published over 20 articles in scholarly journals. He is the former editor of the Journal of Learning Development in Higher Education. [Image Descriptor: Photo of Chris]

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Literature reviews are a necessary step in a research process and often required when writing your research proposal . They involve gathering, analyzing, and evaluating existing knowledge about a topic in order to find gaps in the literature where future studies will be needed.

Ideally, once you have completed your literature review, you will be able to identify how your research project can build upon and extend existing knowledge in your area of study.

Generally, for my undergraduate research students, I recommend a narrative review, where themes can be generated in order for the students to develop sufficient understanding of the topic so they can build upon the themes using unique methods or novel research questions.

If you’re in the process of writing a literature review, I have developed a literature review template for you to use – it’s a huge time-saver and walks you through how to write a literature review step-by-step:

Get your time-saving templates here to write your own literature review.

Literature Review Examples

For the following types of literature review, I present an explanation and overview of the type, followed by links to some real-life literature reviews on the topics.

1. Narrative Review Examples

Also known as a traditional literature review, the narrative review provides a broad overview of the studies done on a particular topic.

It often includes both qualitative and quantitative studies and may cover a wide range of years.

The narrative review’s purpose is to identify commonalities, gaps, and contradictions in the literature .

I recommend to my students that they should gather their studies together, take notes on each study, then try to group them by themes that form the basis for the review (see my step-by-step instructions at the end of the article).

Example Study

Title: Communication in healthcare: a narrative review of the literature and practical recommendations

Citation: Vermeir, P., Vandijck, D., Degroote, S., Peleman, R., Verhaeghe, R., Mortier, E., … & Vogelaers, D. (2015). Communication in healthcare: a narrative review of the literature and practical recommendations. International journal of clinical practice , 69 (11), 1257-1267.

Source: https://onlinelibrary.wiley.com/doi/pdf/10.1111/ijcp.12686  

Overview: This narrative review analyzed themes emerging from 69 articles about communication in healthcare contexts. Five key themes were found in the literature: poor communication can lead to various negative outcomes, discontinuity of care, compromise of patient safety, patient dissatisfaction, and inefficient use of resources. After presenting the key themes, the authors recommend that practitioners need to approach healthcare communication in a more structured way, such as by ensuring there is a clear understanding of who is in charge of ensuring effective communication in clinical settings.

Other Examples

• Burnout in United States Healthcare Professionals: A Narrative Review (Reith, 2018) – read here
• Examining the Presence, Consequences, and Reduction of Implicit Bias in Health Care: A Narrative Review (Zestcott, Blair & Stone, 2016) – read here
• A Narrative Review of School-Based Physical Activity for Enhancing Cognition and Learning (Mavilidi et al., 2018) – read here
• A narrative review on burnout experienced by medical students and residents (Dyrbye & Shanafelt, 2015) – read here

2. Systematic Review Examples

This type of literature review is more structured and rigorous than a narrative review. It involves a detailed and comprehensive plan and search strategy derived from a set of specified research questions.

The key way you’d know a systematic review compared to a narrative review is in the methodology: the systematic review will likely have a very clear criteria for how the studies were collected, and clear explanations of exclusion/inclusion criteria. 

The goal is to gather the maximum amount of valid literature on the topic, filter out invalid or low-quality reviews, and minimize bias. Ideally, this will provide more reliable findings, leading to higher-quality conclusions and recommendations for further research.

You may note from the examples below that the ‘method’ sections in systematic reviews tend to be much more explicit, often noting rigid inclusion/exclusion criteria and exact keywords used in searches.

Title: The importance of food naturalness for consumers: Results of a systematic review  

Citation: Roman, S., Sánchez-Siles, L. M., & Siegrist, M. (2017). The importance of food naturalness for consumers: Results of a systematic review. Trends in food science & technology , 67 , 44-57.

Source: https://www.sciencedirect.com/science/article/pii/S092422441730122X  

Overview: This systematic review included 72 studies of food naturalness to explore trends in the literature about its importance for consumers. Keywords used in the data search included: food, naturalness, natural content, and natural ingredients. Studies were included if they examined consumers’ preference for food naturalness and contained empirical data. The authors found that the literature lacks clarity about how naturalness is defined and measured, but also found that food consumption is significantly influenced by perceived naturalness of goods.

• A systematic review of research on online teaching and learning from 2009 to 2018 (Martin, Sun & Westine, 2020) – read here
• Where Is Current Research on Blockchain Technology? (Yli-Huumo et al., 2016) – read here
• Universities—industry collaboration: A systematic review (Ankrah & Al-Tabbaa, 2015) – read here
• Internet of Things Applications: A Systematic Review (Asghari, Rahmani & Javadi, 2019) – read here

3. Meta-analysis

This is a type of systematic review that uses statistical methods to combine and summarize the results of several studies.

Due to its robust methodology, a meta-analysis is often considered the ‘gold standard’ of secondary research , as it provides a more precise estimate of a treatment effect than any individual study contributing to the pooled analysis.

Furthermore, by aggregating data from a range of studies, a meta-analysis can identify patterns, disagreements, or other interesting relationships that may have been hidden in individual studies.

This helps to enhance the generalizability of findings, making the conclusions drawn from a meta-analysis particularly powerful and informative for policy and practice.

Title: Cholesterol and Alzheimer’s Disease Risk: A Meta-Meta-Analysis

Citation: Sáiz-Vazquez, O., Puente-Martínez, A., Ubillos-Landa, S., Pacheco-Bonrostro, J., & Santabárbara, J. (2020). Cholesterol and Alzheimer’s disease risk: a meta-meta-analysis. Brain sciences, 10(6), 386.

Source: https://doi.org/10.3390/brainsci10060386  

O verview: This study examines the relationship between cholesterol and Alzheimer’s disease (AD). Researchers conducted a systematic search of meta-analyses and reviewed several databases, collecting 100 primary studies and five meta-analyses to analyze the connection between cholesterol and Alzheimer’s disease. They find that the literature compellingly demonstrates that low-density lipoprotein cholesterol (LDL-C) levels significantly influence the development of Alzheimer’s disease.

• The power of feedback revisited: A meta-analysis of educational feedback research (Wisniewski, Zierer & Hattie, 2020) – read here
• How Much Does Education Improve Intelligence? A Meta-Analysis (Ritchie & Tucker-Drob, 2018) – read here
• A meta-analysis of factors related to recycling (Geiger et al., 2019) – read here
• Stress management interventions for police officers and recruits (Patterson, Chung & Swan, 2014) – read here

Other Types of Reviews

• Scoping Review: This type of review is used to map the key concepts underpinning a research area and the main sources and types of evidence available. It can be undertaken as stand-alone projects in their own right, or as a precursor to a systematic review.
• Rapid Review: This type of review accelerates the systematic review process in order to produce information in a timely manner. This is achieved by simplifying or omitting stages of the systematic review process.
• Integrative Review: This review method is more inclusive than others, allowing for the simultaneous inclusion of experimental and non-experimental research. The goal is to more comprehensively understand a particular phenomenon.
• Critical Review: This is similar to a narrative review but requires a robust understanding of both the subject and the existing literature. In a critical review, the reviewer not only summarizes the existing literature, but also evaluates its strengths and weaknesses. This is common in the social sciences and humanities .
• State-of-the-Art Review: This considers the current level of advancement in a field or topic and makes recommendations for future research directions. This type of review is common in technological and scientific fields but can be applied to any discipline.

How to Write a Narrative Review (Tips for Undergrad Students)

Most undergraduate students conducting a capstone research project will be writing narrative reviews. Below is a five-step process for conducting a simple review of the literature for your project.

• Search for Relevant Literature: Use scholarly databases related to your field of study, provided by your university library, along with appropriate search terms to identify key scholarly articles that have been published on your topic.
• Evaluate and Select Sources: Filter the source list by selecting studies that are directly relevant and of sufficient quality, considering factors like credibility , objectivity, accuracy, and validity.
• Analyze and Synthesize: Review each source and summarize the main arguments  in one paragraph (or more, for postgrad). Keep these summaries in a table.
• Identify Themes: With all studies summarized, group studies that share common themes, such as studies that have similar findings or methodologies.
• Write the Review: Write your review based upon the themes or subtopics you have identified. Give a thorough overview of each theme, integrating source data, and conclude with a summary of the current state of knowledge then suggestions for future research based upon your evaluation of what is lacking in the literature.

Literature reviews don’t have to be as scary as they seem. Yes, they are difficult and require a strong degree of comprehension of academic studies. But it can be feasibly done through following a structured approach to data collection and analysis. With my undergraduate research students (who tend to conduct small-scale qualitative studies ), I encourage them to conduct a narrative literature review whereby they can identify key themes in the literature. Within each theme, students can critique key studies and their strengths and limitations , in order to get a lay of the land and come to a point where they can identify ways to contribute new insights to the existing academic conversation on their topic.

Ankrah, S., & Omar, A. T. (2015). Universities–industry collaboration: A systematic review. Scandinavian Journal of Management, 31(3), 387-408.

Asghari, P., Rahmani, A. M., & Javadi, H. H. S. (2019). Internet of Things applications: A systematic review. Computer Networks , 148 , 241-261.

Dyrbye, L., & Shanafelt, T. (2016). A narrative review on burnout experienced by medical students and residents. Medical education , 50 (1), 132-149.

Geiger, J. L., Steg, L., Van Der Werff, E., & Ünal, A. B. (2019). A meta-analysis of factors related to recycling. Journal of environmental psychology , 64 , 78-97.

Martin, F., Sun, T., & Westine, C. D. (2020). A systematic review of research on online teaching and learning from 2009 to 2018. Computers & education , 159 , 104009.

Mavilidi, M. F., Ruiter, M., Schmidt, M., Okely, A. D., Loyens, S., Chandler, P., & Paas, F. (2018). A narrative review of school-based physical activity for enhancing cognition and learning: The importance of relevancy and integration. Frontiers in psychology , 2079.

Patterson, G. T., Chung, I. W., & Swan, P. W. (2014). Stress management interventions for police officers and recruits: A meta-analysis. Journal of experimental criminology , 10 , 487-513.

Reith, T. P. (2018). Burnout in United States healthcare professionals: a narrative review. Cureus , 10 (12).

Ritchie, S. J., & Tucker-Drob, E. M. (2018). How much does education improve intelligence? A meta-analysis. Psychological science , 29 (8), 1358-1369.

Roman, S., Sánchez-Siles, L. M., & Siegrist, M. (2017). The importance of food naturalness for consumers: Results of a systematic review. Trends in food science & technology , 67 , 44-57.

Sáiz-Vazquez, O., Puente-Martínez, A., Ubillos-Landa, S., Pacheco-Bonrostro, J., & Santabárbara, J. (2020). Cholesterol and Alzheimer’s disease risk: a meta-meta-analysis. Brain sciences, 10(6), 386.

Vermeir, P., Vandijck, D., Degroote, S., Peleman, R., Verhaeghe, R., Mortier, E., … & Vogelaers, D. (2015). Communication in healthcare: a narrative review of the literature and practical recommendations. International journal of clinical practice , 69 (11), 1257-1267.

Wisniewski, B., Zierer, K., & Hattie, J. (2020). The power of feedback revisited: A meta-analysis of educational feedback research. Frontiers in Psychology , 10 , 3087.

Yli-Huumo, J., Ko, D., Choi, S., Park, S., & Smolander, K. (2016). Where is current research on blockchain technology?—a systematic review. PloS one , 11 (10), e0163477.

Zestcott, C. A., Blair, I. V., & Stone, J. (2016). Examining the presence, consequences, and reduction of implicit bias in health care: a narrative review. Group Processes & Intergroup Relations , 19 (4), 528-542

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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.

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Methodology

• 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.

Prevent plagiarism. Run a free check.

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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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: 

How to write a good literature review 

• 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.

What is the purpose of literature review?

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: 

a. Habitat Loss and Species Extinction:

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. 

b. Range Shifts and Phenological Changes:

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. 

c. Ocean Acidification and Coral Reefs:

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. 

d. Adaptive Strategies and Conservation Efforts:

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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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. 

Whether you’re exploring a new research field or finding new angles to develop an existing topic, sifting through hundreds of papers can take more time than you have to spare. But what if you could find science-backed insights with verified citations in seconds? That’s the power of Paperpal’s new Research feature!  

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 feature, you get 100% factual insights, with citations backed by 250M+ verified research articles, directly within your writing interface with the option to 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” 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 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.  

Frequently asked questions

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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Introduction

Literature reviews take time. here is some general information to know before you start.  .

•  VIDEO -- This video is a great overview of the entire process.  (2020; North Carolina State University Libraries) --The transcript is included --This is for everyone; ignore the mention of "graduate students" --9.5 minutes, and every second is important  
• OVERVIEW -- Read this page from Purdue's OWL. It's not long, and gives some tips to fill in what you just learned from the video.  
• NOT A RESEARCH ARTICLE -- A literature review follows a different style, format, and structure from a research article.  

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What is a literature review? [with examples]

What is a literature review?

The purpose of a literature review, how to write a literature review, the format of a literature review, general formatting rules, the length of a literature review, literature review examples, frequently asked questions about literature reviews, related articles.

A literature review is an assessment of the sources in a chosen topic of research.

In a literature review, you’re expected to report on the existing scholarly conversation, without adding new contributions.

If you are currently writing one, you've come to the right place. In the following paragraphs, we will explain:

• the objective of a literature review
• how to write a literature review
• the basic format of a literature review

Tip: It’s not always mandatory to add a literature review in a paper. Theses and dissertations often include them, whereas research papers may not. Make sure to consult with your instructor for exact requirements.

The four main objectives of a literature review are:

• Studying the references of your research area
• Summarizing the main arguments
• Identifying current gaps, stances, and issues
• Presenting all of the above in a text

Ultimately, the main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

The format of a literature review is fairly standard. It includes an:

• introduction that briefly introduces the main topic
• body that includes the main discussion of the key arguments
• conclusion that highlights the gaps and issues of the literature

➡️ Take a look at our guide on how to write a literature review to learn more about how to structure a literature review.

First of all, a literature review should have its own labeled section. You should indicate clearly in the table of contents where the literature can be found, and you should label this section as “Literature Review.”

➡️ For more information on writing a thesis, visit our guide on how to structure a thesis .

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, it will be long. If your paper does not depend entirely on references, it will be short.

Take a look at these three theses featuring great literature reviews:

• School-Based Speech-Language Pathologist's Perceptions of Sensory Food Aversions in Children [ PDF , see page 20]
• Who's Writing What We Read: Authorship in Criminological Research [ PDF , see page 4]
• A Phenomenological Study of the Lived Experience of Online Instructors of Theological Reflection at Christian Institutions Accredited by the Association of Theological Schools [ PDF , see page 56]

Literature reviews are most commonly found in theses and dissertations. However, you find them in research papers as well.

There is no set amount of words for a literature review, so the length depends on the research. If you are working with a large amount of sources, then it will be long. If your paper does not depend entirely on references, then it will be short.

No. A literature review should have its own independent section. You should indicate clearly in the table of contents where the literature review can be found, and label this section as “Literature Review.”

The main goal of a literature review is to provide the researcher with sufficient knowledge about the topic in question so that they can eventually make an intervention.

Literature Review Guide: Examples of Literature Reviews

• What is a Literature Review?
• How to start?
• Picking your research question and searching
• Search strategies and Databases
• How to organise the review
• Examples of Literature Reviews
• Library summary

All good quality journal articles will include a small Literature Review after the Introduction paragraph.  It may not be called a Literature Review but gives you an idea of how one is created in miniature.

Sample Literature Reviews as part of a articles or Theses

• Hackett, G and Melia, D . The hotel as the holiday/stay destination:trends and innovations. Presented at TRIC Conference, Belfast, Ireland- June 2012 and EuroCHRIE Conference

Links to sample Literature Reviews from other libraries

• Sample literature reviews from University of West Florida

Irish Theses

• Phillips, Martin (2015) European airline performance: a data envelopment analysis with extrapolations based on model outputs. Master of Business Studies thesis, Dublin City University.
• The customers’ perception of servicescape’s influence on their behaviours, in the food retail industry : Dublin Business School 2015
• Coughlan, Ray (2015) What was the role of leadership in the transformation of a failing Irish Insurance business. Masters thesis, Dublin, National College of Ireland.
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YSN Doctoral Programs: Steps in Conducting a Literature Review

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• Steps in Conducting a Literature Review

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.

APA7 Style resources

APA Style Blog - for those harder to find answers

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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What Is A Literature Review?

A plain-language explainer (with examples).

By:  Derek Jansen (MBA) & Kerryn Warren (PhD) | June 2020 (Updated May 2023)

If you’re faced with writing a dissertation or thesis, chances are you’ve encountered the term “literature review” . If you’re on this page, you’re probably not 100% what the literature review is all about. The good news is that you’ve come to the right place.

Literature Review 101

• What (exactly) is a literature review
• What’s the purpose of the literature review chapter
• How to find high-quality resources
• How to structure your literature review chapter
• Example of an actual literature review

What is a literature review?

The word “literature review” can refer to two related things that are part of the broader literature review process. The first is the task of  reviewing the literature  – i.e. sourcing and reading through the existing research relating to your research topic. The second is the  actual chapter  that you write up in your dissertation, thesis or research project. Let’s look at each of them:

Reviewing the literature

The first step of any literature review is to hunt down and  read through the existing research  that’s relevant to your research topic. To do this, you’ll use a combination of tools (we’ll discuss some of these later) to find journal articles, books, ebooks, research reports, dissertations, theses and any other credible sources of information that relate to your topic. You’ll then  summarise and catalogue these  for easy reference when you write up your literature review chapter. 

The literature review chapter

The second step of the literature review is to write the actual literature review chapter (this is usually the second chapter in a typical dissertation or thesis structure ). At the simplest level, the literature review chapter is an  overview of the key literature  that’s relevant to your research topic. This chapter should provide a smooth-flowing discussion of what research has already been done, what is known, what is unknown and what is contested in relation to your research topic. So, you can think of it as an  integrated review of the state of knowledge  around your research topic. 

What’s the purpose of a literature review?

The literature review chapter has a few important functions within your dissertation, thesis or research project. Let’s take a look at these:

Purpose #1 – Demonstrate your topic knowledge

The first function of the literature review chapter is, quite simply, to show the reader (or marker) that you  know what you’re talking about . In other words, a good literature review chapter demonstrates that you’ve read the relevant existing research and understand what’s going on – who’s said what, what’s agreed upon, disagreed upon and so on. This needs to be  more than just a summary  of who said what – it needs to integrate the existing research to  show how it all fits together  and what’s missing (which leads us to purpose #2, next). 

Purpose #2 – Reveal the research gap that you’ll fill

The second function of the literature review chapter is to  show what’s currently missing  from the existing research, to lay the foundation for your own research topic. In other words, your literature review chapter needs to show that there are currently “missing pieces” in terms of the bigger puzzle, and that  your study will fill one of those research gaps . By doing this, you are showing that your research topic is original and will help contribute to the body of knowledge. In other words, the literature review helps justify your research topic.  

Purpose #3 – Lay the foundation for your conceptual framework

The third function of the literature review is to form the  basis for a conceptual framework . Not every research topic will necessarily have a conceptual framework, but if your topic does require one, it needs to be rooted in your literature review. 

For example, let’s say your research aims to identify the drivers of a certain outcome – the factors which contribute to burnout in office workers. In this case, you’d likely develop a conceptual framework which details the potential factors (e.g. long hours, excessive stress, etc), as well as the outcome (burnout). Those factors would need to emerge from the literature review chapter – they can’t just come from your gut! 

So, in this case, the literature review chapter would uncover each of the potential factors (based on previous studies about burnout), which would then be modelled into a framework. 

Purpose #4 – To inform your methodology

The fourth function of the literature review is to  inform the choice of methodology  for your own research. As we’ve  discussed on the Grad Coach blog , your choice of methodology will be heavily influenced by your research aims, objectives and questions . Given that you’ll be reviewing studies covering a topic close to yours, it makes sense that you could learn a lot from their (well-considered) methodologies.

So, when you’re reviewing the literature, you’ll need to  pay close attention to the research design , methodology and methods used in similar studies, and use these to inform your methodology. Quite often, you’ll be able to  “borrow” from previous studies . This is especially true for quantitative studies , as you can use previously tried and tested measures and scales. 

How do I find articles for my literature review?

Finding quality journal articles is essential to crafting a rock-solid literature review. As you probably already know, not all research is created equally, and so you need to make sure that your literature review is  built on credible research . 

We could write an entire post on how to find quality literature (actually, we have ), but a good starting point is Google Scholar . Google Scholar is essentially the academic equivalent of Google, using Google’s powerful search capabilities to find relevant journal articles and reports. It certainly doesn’t cover every possible resource, but it’s a very useful way to get started on your literature review journey, as it will very quickly give you a good indication of what the  most popular pieces of research  are in your field.

One downside of Google Scholar is that it’s merely a search engine – that is, it lists the articles, but oftentimes  it doesn’t host the articles . So you’ll often hit a paywall when clicking through to journal websites. 

Thankfully, your university should provide you with access to their library, so you can find the article titles using Google Scholar and then search for them by name in your university’s online library. Your university may also provide you with access to  ResearchGate , which is another great source for existing research. 

Remember, the correct search keywords will be super important to get the right information from the start. So, pay close attention to the keywords used in the journal articles you read and use those keywords to search for more articles. If you can’t find a spoon in the kitchen, you haven’t looked in the right drawer. 

Need a helping hand?

How should I structure my literature review?

Unfortunately, there’s no generic universal answer for this one. The structure of your literature review will depend largely on your topic area and your research aims and objectives.

You could potentially structure your literature review chapter according to theme, group, variables , chronologically or per concepts in your field of research. We explain the main approaches to structuring your literature review here . You can also download a copy of our free literature review template to help you establish an initial structure.

In general, it’s also a good idea to start wide (i.e. the big-picture-level) and then narrow down, ending your literature review close to your research questions . However, there’s no universal one “right way” to structure your literature review. The most important thing is not to discuss your sources one after the other like a list – as we touched on earlier, your literature review needs to synthesise the research , not summarise it .

Ultimately, you need to craft your literature review so that it conveys the most important information effectively – it needs to tell a logical story in a digestible way. It’s no use starting off with highly technical terms and then only explaining what these terms mean later. Always assume your reader is not a subject matter expert and hold their hand through a journe y of the literature while keeping the functions of the literature review chapter (which we discussed earlier) front of mind.

Example of a literature review

In the video below, we walk you through a high-quality literature review from a dissertation that earned full distinction. This will give you a clearer view of what a strong literature review looks like in practice and hopefully provide some inspiration for your own. 

Wrapping Up

In this post, we’ve (hopefully) answered the question, “ what is a literature review? “. We’ve also considered the purpose and functions of the literature review, as well as how to find literature and how to structure the literature review chapter. If you’re keen to learn more, check out the literature review section of the Grad Coach blog , as well as our detailed video post covering how to write a literature review . 

Psst… there’s more!

This post is an extract from our bestselling short course, Literature Review Bootcamp . If you want to work smart, you don't want to miss this .

16 Comments

Thanks for this review. It narrates what’s not been taught as tutors are always in a early to finish their classes.

Thanks for the kind words, Becky. Good luck with your literature review 🙂

This website is amazing, it really helps break everything down. Thank you, I would have been lost without it.

This is review is amazing. I benefited from it a lot and hope others visiting this website will benefit too.

Timothy T. Chol [email protected]

Thank you very much for the guiding in literature review I learn and benefited a lot this make my journey smooth I’ll recommend this site to my friends

This was so useful. Thank you so much.

Hi, Concept was explained nicely by both of you. Thanks a lot for sharing it. It will surely help research scholars to start their Research Journey.

The review is really helpful to me especially during this period of covid-19 pandemic when most universities in my country only offer online classes. Great stuff

Great Brief Explanation, thanks

So helpful to me as a student

GradCoach is a fantastic site with brilliant and modern minds behind it.. I spent weeks decoding the substantial academic Jargon and grounding my initial steps on the research process, which could be shortened to a couple of days through the Gradcoach. Thanks again!

This is an amazing talk. I paved way for myself as a researcher. Thank you GradCoach!

Well-presented overview of the literature!

This was brilliant. So clear. Thank you

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Writing a Literature Review: Examples & Tutorials

• Phase 1: Scope of Review
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Examples of Lit. Reviews

Sample Literature Review -Here is a sample literature review written by a librarian at American University Library.

Deshmukh, Marion F. " The Visual Arts and Cultural Migration in the 1930s and 1940s: A Literature Review. " Central European History (Cambridge University Press / UK) 41.4 (2008): 569-604. Dunjó, Jordi, et al. " Hazard and Operability (HAZOP) Analysis. A Literature Review ." Journal of Hazardous Materials 173.1-3 (2010): 19-32. Gibbons, Susan. " Understanding Empathy as a Complex Construct: A Review of the Literature ." Clinical Social Work Journal 39.3 (2011): 243-52.

Liddle, H. A. (2004). Family-based therapies for adolescent alcohol and drug use: Research contributions and future research needs.   Addiction , 99 (Suppl.2), 76-92.

Mayer, David J. " Acupuncture: An Evidence-Based Review of the Clinical Literature ." Annual Review of Medicine 51:1 (2000): 49-63.

Meyer, Sebastian, Bruno Glaser, and Peter Quicker. " Technical, Economical, and Climate-Related Aspects of Biochar Production Technologies: A Literature Review. " Environmental science & technology 45.22 (2011): 9473-83.

• Writing the Literature Review Part I Defines what a literature review is - and is not.
• Writing the Literature Review Part II Organizing sources, basic steps in the writing process.
• Literature Review Overview for Graduate Students Understand how studies relate to one another, how your own ideas fit within the existing literature.
• Interactive tutorial for literature reviews in Education & Behavioral Sciences • Understanding the Literature Review • Identifying Sources for the Literature Review • Finding Review and Research Articles • Putting it All Together

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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.

Literature Review

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What is a literature review?

Why conduct a literature review, stages of a literature review, lit reviews: an overview (video), check out these books.

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• 2. Plan your search
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Definition: A literature review is a systematic examination and synthesis of existing scholarly research on a specific topic or subject.

Purpose: It serves to provide a comprehensive overview of the current state of knowledge within a particular field.

Analysis: Involves critically evaluating and summarizing key findings, methodologies, and debates found in academic literature.

Identifying Gaps: Aims to pinpoint areas where there is a lack of research or unresolved questions, highlighting opportunities for further investigation.

Contextualization: Enables researchers to understand how their work fits into the broader academic conversation and contributes to the existing body of knowledge.

tl;dr  A literature review critically examines and synthesizes existing scholarly research and publications on a specific topic to provide a comprehensive understanding of the current state of knowledge in the field.

What is a literature review NOT?

❌ An annotated bibliography

❌ Original research

❌ A summary

❌ Something to be conducted at the end of your research

❌ An opinion piece

❌ A chronological compilation of studies

The reason for conducting a literature review is to:

Literature Reviews: An Overview for Graduate Students

While this 9-minute video from NCSU is geared toward graduate students, it is useful for anyone conducting a literature review.

Writing the literature review: A practical guide

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Writing literature reviews: A guide for students of the social and behavioral sciences

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So, you have to write a literature review: A guided workbook for engineers

Telling a research story: Writing a literature review

The literature review: Six steps to success

Systematic approaches to a successful literature review

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WTO / Education / 39 Best Literature Review Examples (Guide with Samples)

39 Best Literature Review Examples (Guide with Samples)

A literature review is a compilation of current knowledge on a particular topic derived from the critical evaluation of different scholarly sources such as books, articles, and publications, which is then presented in an organized manner to relate to a specific research problem being investigated.

It highlights the methods, relevant theories, and gaps in existing research on a particular subject. It can be both a summary and synthesis of information on a specific topic. A summary reiterates key information from scholarly sources, while synthesis is a new interpretation or combination of new and old material. 

As a synthesis, it can outline the intellectual progression of knowledge in a particular field or topic, which might involve stating key debates throughout the advancement period.  

Literature Review Examples

Purpose of Literature Review

Literature reviews have different purposes in scholarly articles, research papers , and books, depending on the discipline at hand. First and foremost, reviews are generally meant to showcase the extensive research carried out by an author on a particular topic and their findings, which will form the foundation of the research. It then summarizes the information to show the author’s familiarity with the topic in question.

The review also demonstrates the relationship between the topic being investigated and other topics that were under consideration. Finally, it outlines the gaps in the previous works of other scholars, which create areas of research.

Literature reviews provide a new interpretation of previous scholarly publications and aim to resolve conflicting studies done in the past. In addition, identifying existing gaps in a particular research area illustrates the starting point of the research.

Literature Review vs. Academic Research Paper

A research paper presents new ideas, arguments, and approaches toward a particular topic. The conclusions of a research paper will be based on the analysis and interpretation of raw data collected by the author and an original study. On the other hand, a literature review is based on the findings of other publications. Thus, the review highlights the author’s understanding of a topic based on the previously conducted research. It is part of a research paper.

Where, When, and Why

The need for a literature review in a publication will vary from one situation to the other and the field/discipline of research. These two factors determine what is expected from the lit review. For example, a scientific review will be more analytical on the methods and results of previous research. In contrast, a philosophical review will be more argumentative, highlighting the discrepancies and correspondences between scholars.

It can either be part of a publication or a stand-alone document. As part of a research publication, it is often placed after the introduction to the topic outlining knowledge about a particular topic and critical sources that formed the foundation of the research. As an individual document, it is prepared by students as part of course study to aid the students in familiarizing themselves with different topics in their field of study.

Lit reviews also guide students to help them synthesize theoretical methodologies and frameworks to adopt in academic research . As a publication, literature reviews are used to document existing information about a topic for readers (other scholars) to go through for whatever reasons they may have. Published studies are essentially helpful to new scholars getting into any field of research.

Types of Literature Review

Before looking into how to write a literature review, it is vital to understand the different types. The type will usually depend on the objective approach of the author.

Common types are:  

Argumentative review

An argumentative review is adopted when the research paper or publication is meant to take a contrarian viewpoint on a particular subject. The review analyses an existing argument, philosophical problem, assumption, or conclusion outlined in different studies with an objective to either support or oppose the argument. 

Integrative review

An integrative review integrates secondary data to develop new perspectives and frameworks on a topic. This is more prevalent in research that does not involve primary data. In addition, integrative reviews are more familiar with social sciences.       

Historical review

Historical reviews are used when scholars or authors place a particular idea, concept, theory, or research in a historical context. It examines the idea, theory, or issue from the first time it was discussed and outlines its evolution throughout a given period.  

Methodological review

Methodological reviews look at how a specific theory, concept, results, or findings were developed. Therefore, methodological reviews will analyze the different methods used by different scholars to arrive at conclusions or knowledge about the topic being investigated.

Some of the methods scholars use in different disciplines to obtain information are interviewing, sampling, practical experiments/data collection, research approaches, critical thinking, social experiments, etc.

Methodological reviews are hence used to discuss tested methods of research and ethics that a researcher should be aware of before undertaking their investigations.  

Systematic review

A systematic review is a more detailed and comprehensive review compared to other types of lit reviews. It highlights any existing research evidence associated with a clearly defined research problem or question. The evidence is collected, analyzed, and reported in a summarized but detailed manner. Systematic reviews are popularly presented as a cause-and-effect structure.

Theoretical review

A theoretical review delves into the different theories regarding a particular issue, challenge, concept, or theory. It identifies their inadequacy in explaining the issue or concept at hand. The review then identifies the relationships between the identified theories, and the degree of research done and poses novel hypotheses to be investigated.

Organization of a Literature Review

How an author organizes a literature review will depend on what they aim to achieve. As a consequence, there are multiple ways of organizing it which are discussed below:

Chronological 

A chronological format outlines knowledge on a particular topic based on when the scholarly source of information was published. Starting with the earliest followed up to the most recent chronological order. This format should be used if there is a clear chronological order in the development of the information; therefore, it will not be applicable in some cases. Instead, key turning points, patterns, and events that impacted the direction of the knowledge should be outlined.  

By publication

It can be organized in the scholarly publications reviewed by the author, scholar, or student. The by-publication format should only improve the review and facilitate what the author aims to accomplish. 

Scholars or students can adopt a dominant trend in research, such as history, developmental stages, steps involved in a process, etc.

Methodological

A methodological format is based on the methods used by the researcher. Thus, the order of contents in the lit review will depend on the method they will use to carry out their research, knowledge obtained from the first method appears first, and the rest of the information follows in the same order according to the methods used by the author.  

Literature reviews organized in a thematic format revolve around the subject being investigated in no order. It is, therefore, ordinarily up to the researcher or author to determine how they intend to outline the information. A thematic format will crossover from one period and publication to another, but can sometimes incorporate a chronological order.

Theoretical

Literature reviews organized in a theoretical format have their contents organized in an abstract framework established by the author to discuss different concepts, theories, and concepts and how they relate to the research at hand.

Additional sections

Depending on the objective, other sections do not fit under conventional lit review formats that one may need to add. Below are some of the sections that authors or students can include in the lit review:

• Current situation: The review can have information about the current state of things regarding the topic at hand to facilitate further understanding.
• History: Researchers can summarize the subject under investigation, literature, or concept if the review is not already in chronological format.
• Selection methods: Lit reviews are known to outline the methods or criteria used in selecting the way to present information and scholarly sources referenced in the review.
• Standards: it can also include the standards used in choosing the format to present information in the review and the scholarly literature used in the research.
• Further questions for research: The review can include questions emanating from the review and how the researcher will further explore their research to address the queries raised.

Literature Review Samples

Considerations Before Writing a Literature Review

Preparation is essential when it comes to writing. The objective should be to come up with a review that satisfactorily explores the topic being discussed. The following considerations are steps towards that if incorporated into the writing process:

Authors should seek clarification from mentors or supervisors before commencing the writing process. First, determine what is expected from the lit review. The type and number of sources to be used, the assignment (summarize, synthesize, or critique), and the type of information provided should be clear.

Find models

You should review literature from other authors in the same discipline and evaluate how those authors presented their lit reviews. Previous lit reviews can be used as guides that point authors in the right direction when writing their lit reviews.

Narrow your topic

It is always advantageous to narrow down the research topic to a specific area of research; that way, the number of sources can also be reduced. Even though conducting research will usually involve extensive research on all available materials about a particular topic, having a well-defined topic simplifies the task at hand.

Current sources

Determine if the research project or discipline ought to be based on the most recent findings or information. It is common for knowledge to become obsolete, especially in disciplines where discoveries and new inventions are made fast. If the lit review should be based on current knowledge, limit the sources to the most recent literature. Some disciplines will typically have a limit on how old the sources should be.  

How to Write a Literature Review (Expert Guide)

Once all pre-writing considerations have been taken into account, it is time to write the document. At this point, you should already be aware of what you wish to accomplish with the literature review, and the steps to writing an exemplary lit review are mentioned below:

Problem formulation

First and foremost, clearly define the topic (research area) to be investigated. For students, this will sometimes be given as an assignment. However, the research could be an academic project, which means that the author has to come up with the problem and define it themselves.

Search for relevant studies

Once the problem is clearly expressed, you should search for studies related to the topic, concept, theory, or idea and questions surrounding the topic. Most stand-alone lit reviews will generally attempt to answer a more concentrated question. On the internet, literature can be searched using keywords related to the research area. In addition to keywords, include vital variables such as synonyms and associated terms. The inclusion of Boolean operators and, or not, is also used to narrow down results to more specific publications.

Familiar sources for publications are:

• Google Scholar
• Library catalogue
• Econ lit (economics)
• Project Muse (humanities and social sciences)
• Inspec (physics, engineering, and computer science )
• Medline (life sciences and biomedicine)

Before selecting relevant studies, go through their abstract and determine if they fit the scope needed in the investigation. Use a list to note down any chosen works. Select landmark sources in the discipline.

Evaluation of sources/data

The next step is the evaluation stage . Evaluation involves a lot of reading. Evaluation can be done in two stages; overall skimming and thorough reading. During the second stage of this step, be critical, ask questions, and take many notes.

Some of the questions authors or researchers should ask themselves are:

• What is the author’s objective? What problem, concept, or theory are they putting across?
• What are the main concepts?
• What are the methodologies used by the author to arrive at the results and conclusions?
• What are the strengths and weaknesses of the results and conclusions?

Use credible sources. Most cited sources are preferred as they indicate their influence in the field. Also, keep track of the citations to be later incorporated.

Identify themes, debates, and gaps

While reading the sources, identify key patterns, themes, debates/arguments, and gaps in each literature. These elements help tie the literature to the topic under investigation. Look for consistent patterns, themes, questions, challenges, methods, and inconsistencies in the same. Consistencies present critical information for consideration, while inconsistencies present opportunities for research areas.

Outline the structure

Formatting is part and parcel of a well-written work. Selecting the structure should start by creating an outline with all the information that will go into the lit review, then consider the different types of structures and select the most suitable. Next, take the basic structure of the introduction, body, and conclusion into consideration and start work from there. 

Analysis and interpretation 

Lastly, perform an in-depth analysis and interpretation of the information obtained from the scholarly research and put it into writing. The summarized, synthesized, and critically evaluated information is then written down in well-structured paragraphs that follow the chosen structure. Transition words are used to draw comparisons, connections, and contrasts.

Format 

Ordinarily, a literature review will have three key components: introduction, body, and conclusion. These components should appear in the document in the following order:

Introduction

An introduction should inform the reader which topic is being studied. It gives the reader an overall idea of the purpose and focus of the document. The introduction lets the reader know beforehand the key things that will be highlighted in the document. Therefore, the introduction should be brief and precise.

The next item is the body, where the primary purpose of the lit review is fulfilled. The body should take critical information from all the sources used and comprehensively present them. This is where the author reports the extensive analysis and interpretation results that they gathered from all the sources they reviewed. The body should be categorized into themes, ideas, and concepts within the main topic.

Lastly, a summary of what the lit review entails should be provided as a conclusion. The critical points obtained from examining the sources should be written down and linked to the primary subject of the review. Key points are those that have the most outstanding contribution to the research.

Studies used should be screened based on provenance (author’s credentials or credibility), methodology, objectivity, persuasiveness, and value related to the topic at hand.

Guidelines for Writing a Literature Review

To improve the delivery of information, there are certain elements that authors can incorporate. They are:

Use evidence

The lit review’s findings, interpretations, and general contents should be based on actual evidence or credible literature. Using citations is evidence of authentic information.

Be selective

There will always be a lot of information available from the reviewed sources. Authors should therefore be selective and discuss the key points that focus on the topic. Not all information must be included in the review.  

Word-for-word quotes are acceptable . This is even more so if a critical point or author-specific terminology or knowledge cannot be paraphrased. Quotes should, however, be used sparingly.

Summarize and synthesize

The information obtained from the sources should be summarized, and the author should use it to synthesize new arguments, concepts, or ideas related to their research.

Keep your voice

The literature review should reflect the author’s voice as it is a review of other people’s works. This can be done by starting and ending the paragraphs with an original voice, ideas, and wordings.

Use caution while paraphrasing

Any paraphrased information should be conveyed accurately and in the author’s words. A citation must always be done, even when paraphrasing has been done.

Proofread before submitting or publishing. Go through the document a few times and make the necessary changes. The review should be within the applicable guidelines. Check for language and any other errors and edit accordingly.

Do’s and Don’ts for a Literature Review 

Every researcher wants to introduce their readers to a particular topic in an informative and engaging manner. Below are tips that can be used to this effect.

The following things should be opted by the researcher when writing a lit review:

• Find a focus: Authors should take a direction, idea, concept, or argument and stick to it. The information conveyed should then be made to align with the chosen point of focus. Thus, the review is not simply a list of analyzed sources, but a detailed summary of how different sources have a focal point (intertwined).
• Well-chosen sources: The quality of the information will, to a great extent, be determined by the quality of sources used. Therefore, take time to select suitable sources and more value will be added to the review.
• Create an annotated bibliography: Creating an annotated bibliography is recommended as one reads their sources. The bibliography keeps track of sources and takes notes. This information can be used when writing the final lit review.
• Synthesize research: Information obtained from the relevant studies should be combined to come up with new or original ideas. You should present a new domain based on previous sources’ knowledge, not just restating the information.
• Argumentative approach: Well-written literature reviews will often argue to support an author’s stance on a particular topic. The author can choose to address how the author’s work is filling a particular gap or support one of the scholar’s arguments and perception towards a particular topic. However, this argumentative approach will not work in all situations; it is usually discipline-specific. 
• Convey it to the reader: It should let the reader know the document’s main idea, concept, or argument. This can be done by including a simple statement that compels the reader to think precisely and know what to expect.
• Break out your disciplinary box: The research will often be multi-disciplinary. Literature reviews should then collect interdisciplinary information from multiple sources as they add novel dynamics to the topic under investigation. It should be noted that this does not imply that the researcher should substitute the literature from the topic’s discipline with that from other disciplines. This is usually an improvement strategy that adds substance to the review.
• Look for repeated patterns: Be attentive to pick out repeated ideas, findings, and concepts from different scholars as they will often illustrate agreed research dead-end or a scholarly conclusion.
• Don’t just review for content: When reviewing the literature, examine the content and other writing and presentation techniques. Look out for unique ways information has been presented, methods used, consistent citations, and non-textual elements such as graphs, and figures used to present information. In addition, the researcher identifies theories used to predict, explain, or understand phenomena within the discipline.
• Search Web of Science and Google Scholar: Conduct citation tracking about the leading scholars already identified in the search process. Scholars cited by multiple scholars outside the principal discipline will generally indicate that there are no new publications on the topic.

The following don’ts should be avoided:

• Do not select studies that are not directly related to the topic being investigated.
• Avoid rushing when identifying and selecting sources to use to research the problem.
• Avoid the use of secondary analytical sources. Instead, opt to use sources with primary research studies or data. Secondary analytical sources will often cite primary analytical sources; research should refer to them instead.
• Do not accept other scholarly findings, theories, or interpretations without critically examining and critiquing them.
• Researchers should not outline the search procedures used to identify scholarly sources for reviewing purposes.
• Avoid including isolated statistical findings without illustrating how they were arrived at using chi-squared or meta-analytic methods.
• Do not review studies that only validate the assumptions, stances, and concepts of your thesis; consider contradicting works with alternative and conflicting stances.

Frequently Asked Questions

It is written by researchers, authors, and students who must study literature to gather knowledge on a particular topic they are interested in.

It should be placed right after the introduction of the dissertation. It places the research in a scholarly context by summarizing existing knowledge on the particular topic.

Researchers and authors are not limited in terms of how many sources they can review. Students will usually have a given number of sources to review as an assignment. However, the number of sources referenced in a lit review will vary from one topic or discipline to the other. Some topics have a vast catalog of available sources, while others have minimal sources, especially emerging issues. It is, however, advised that each key point discussed should have at least 2-3 references/sources. For example, a 10-page lit review will have an average of 30 references.

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https://educationhub.blog.gov.uk/2024/08/20/gcse-results-day-2024-number-grading-system/

GCSE results day 2024: Everything you need to know including the number grading system

Thousands of students across the country will soon be finding out their GCSE results and thinking about the next steps in their education.   

Here we explain everything you need to know about the big day, from when results day is, to the current 9-1 grading scale, to what your options are if your results aren’t what you’re expecting.  

When is GCSE results day 2024?  

GCSE results day will be taking place on Thursday the 22 August.     

The results will be made available to schools on Wednesday and available to pick up from your school by 8am on Thursday morning.  

Schools will issue their own instructions on how and when to collect your results.   

When did we change to a number grading scale?  

The shift to the numerical grading system was introduced in England in 2017 firstly in English language, English literature, and maths.  

By 2020 all subjects were shifted to number grades. This means anyone with GCSE results from 2017-2020 will have a combination of both letters and numbers.  

The numerical grading system was to signal more challenging GCSEs and to better differentiate between students’ abilities - particularly at higher grades between the A *-C grades. There only used to be 4 grades between A* and C, now with the numerical grading scale there are 6.  

What do the number grades mean?  

The grades are ranked from 1, the lowest, to 9, the highest.  

The grades don’t exactly translate, but the two grading scales meet at three points as illustrated below.  

The bottom of grade 7 is aligned with the bottom of grade A, while the bottom of grade 4 is aligned to the bottom of grade C.    

Meanwhile, the bottom of grade 1 is aligned to the bottom of grade G.  

What to do if your results weren’t what you were expecting?  

If your results weren’t what you were expecting, firstly don’t panic. You have options.  

First things first, speak to your school or college – they could be flexible on entry requirements if you’ve just missed your grades.   

They’ll also be able to give you the best tailored advice on whether re-sitting while studying for your next qualifications is a possibility.   

If you’re really unhappy with your results you can enter to resit all GCSE subjects in summer 2025. You can also take autumn exams in GCSE English language and maths.  

Speak to your sixth form or college to decide when it’s the best time for you to resit a GCSE exam.  

Look for other courses with different grade requirements     

Entry requirements vary depending on the college and course. Ask your school for advice, and call your college or another one in your area to see if there’s a space on a course you’re interested in.    

Consider an apprenticeship    

Apprenticeships combine a practical training job with study too. They’re open to you if you’re 16 or over, living in England, and not in full time education.  

As an apprentice you’ll be a paid employee, have the opportunity to work alongside experienced staff, gain job-specific skills, and get time set aside for training and study related to your role.   

You can find out more about how to apply here .  

Talk to a National Careers Service (NCS) adviser    

The National Career Service is a free resource that can help you with your career planning. Give them a call to discuss potential routes into higher education, further education, or the workplace.   

Whatever your results, if you want to find out more about all your education and training options, as well as get practical advice about your exam results, visit the  National Careers Service page  and Skills for Careers to explore your study and work choices.   

You may also be interested in:

• Results day 2024: What's next after picking up your A level, T level and VTQ results?
• When is results day 2024? GCSEs, A levels, T Levels and VTQs

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Radiographic characterization of OPLL progression in patients receiving laminoplasty with a minimum of two-years follow-up

• Open access
• Published: 29 August 2024
• Volume 47 , article number  505 , ( 2024 )

Cite this article

You have full access to this open access article

• Wai Kiu Thomas Liu 1 ,
• Keira Ho Yuet Siu 1 ,
• Jason Pui-Yin Cheung 1 &
• Graham Ka-Hon Shea 1  

Ossification of the posterior longitudinal ligament (OPLL) is a common cause of degenerative cervical myelopathy (DCM) in Asian populations. Characterization of OPLL progression following laminoplasty remains limited in the literature. 29 patients with OPLL received cervical laminoplasty and a minimum of 2-years follow-up. Clinical and radiological surveillance occurred at 3-months, 6-months, 12-months post-op and then at yearly intervals. Transverse (anteroposterior) diameter and sagittal length of OPLL in relation to their cervical vertebral level of localisation was assessed upon immediate post-op radiographs compared to those obtained at subsequent follow-up. OPLL progression was defined as an increase in transverse dimensions and/or length by ≥ 2 mm. The average period of clinical follow-up was 6.7 ± 3.3 years. Upon latest follow-up, 79% of patients demonstrated at least 2 mm of transverse or longitudinal progression of OPLL. This corresponded to 2-years and 5-year progression rates of 54% and 71% respectively. OPLL located over C5 demonstrated the greatest transverse progression rate at (0.24 ± 0.34 mm / year). The mean overall longitudinal progression rate was 1.61 ± 2.06 mm / year. No patients experienced neurological decline resulting from OPLL progression requiring revision decompression during the period of post-operative observation. Characterizing transverse and longitudinal progression by cervical level via radiographs has implications in surgical planning for OPLL and should be consolidated upon post-operative CT/MRI scans as well as larger sample sizes.

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Ossification of the posterior longitudinal ligament (OPLL) is a cause of degenerative cervical myelopathy (DCM) that is particularly common in East Asian countries, with a population prevalence of 0.4 to 3.0% [ 1 , 2 ]. OPLL most often affects the C4 to C6 cervical levels, whilst classification is according to radiographic findings and includes continuous, mixed, segmental, and localized subtypes [ 1 ]. Continuous and mixed OPLL have been shown to be associated with higher rates of progression [ 3 , 4 ]. The exact pathogenesis of OPLL is unclear but suggested to be secondary to both genetic and environmental factors [ 5 ]. Single-nucleotide polymorphism (SNP) of collagen genes have been implicated in pathogenesis [ 6 , 7 ] whilst dysfunction of human nucleotide pyrophosphatase (NPPS) is proposed to exacerbate tissue calcification [ 8 ]. In addition to genetic factors, mechanical stress is a risk factor [ 9 ].

The current standard of care in the treatment of OPLL with neurological impairment is to offer surgical decompression. Direct anterior decompression may be more difficult to achieve when the ossified segment lies posterior to the vertebral body thereby requiring a corpectomy, and as adhesions between the OPLL and ventral dura increases the risk of dural tear and CSF leak [ 10 , 11 ]. Therefore, when cervical spine alignment is favourable [ 12 ], indirect decompression via a posterior approach is may be preferred particularly in multilevel and/or congenital canal stenosis. For both anterior and posterior approaches, there is the concern that OPLL progression following surgery could lead to recurrence of compression followed by neurological deterioration.

With regards to posterior cervical surgery for OPLL, a recent meta-analysis of laminoplasty in comparison to laminectomy and fusion demonstrated similar neurological outcomes and range of motion after surgery. Shorter operation time and less blood loss was demonstrable following laminoplasty whilst cervical lordotic angle was higher following fusion [ 13 ]. It has been reported that up to 70% of patients exhibit progression of OPLL following laminoplasty due to sparing of cervical motion [ 14 ]. Nevertheless, recommending laminectomy and fusion when OPLL is treated via a posterior approach remains controversial as some authors have conversely demonstrate increased ossification following fusion [ 15 ], the clinical significance of post-operative OPLL progression remains conflicting [ 3 , 4 ], and outcomes at 2-years following laminoplasty remain good in spite of OPLL progression [ 16 ]. An additional issue that remains unknown is how OPLL progression differs by cervical level, which has implications on surgical approach, planning, and execution. To address these issues, this study investigated the rates of radiological OPLL progression according to cervical level in patients receiving laminoplasty, with an average post-operative follow-up period exceeding 6-years.

Patient recruitment and follow-up

This study was approved by the Institutional Review Board (IRB) of our institution and conducted according to the principles detailed in the Preferred Reporting Of CasE Series in Surgery (PROCESS) Guidelines. We identified patients with DCM and radiological evidence of cervical canal narrowing due to OPLL who had undergone cervical laminoplasty between 1 November 2009 and 31 September 2019 at an academic spinal unit. At our centre, we favour laminoplasty for indirect decompression in patients with cervical OPLL and a stable lordotic cervical spine. Our rationale for favouring laminoplasty over laminectomy and posterior fusion is due to its motion-sparing nature and non-inferior clinical outcomes together with lower risk of C5 palsy [ 17 , 18 , 19 ]. Open door laminoplasties were performed as previously described, with a full-thickness trough made at the junction of the laminae and lateral mass on one side, and a partial-thickness trough over the contralateral side to allow for lamina opening [ 20 ]. Upon discharge, patients were assessed at 2-weeks to review the wound condition, then at 3-months, 6-months, 12-months and yearly intervals for clinical and radiologically monitoring. We excluded patients suffering from DCM secondary to other causes, patients without radiological evidence of OPLL upon lateral cervical X-rays, patients having received previous cervical spinal operations, patients with neurological deterioration associated with traumatic cervical injury, and patients with less than 2 years of clinical and radiological follow-up. 80 patients with an operative diagnosis of ossified posterior longitudinal ligament who underwent cervical laminoplasty in the abovementioned period were identified using the Clinical Data Analysis and Reporting System of the Hospital Authority, Hong Kong. A flowchart for patient recruitment, resulting in 29 patients included for analysis, is shown in Fig.  1 .

Flowchart for patient recruitment

Demographic data, including age at operation, gender, details of the laminoplasty procedure, pre- and post-operative neurological function (modified JOA score) [ 21 ] and occurrence of any surgical complications (infection, hardware malposition, neurological deterioration) were retrieved from electronic medical records. Lateral cervical x-rays from pre- and post-operative periods, as well as pre-op cervical MRIs, were retrieved from the hospital picture archiving and communication system (PACS).

Measurement of OPLL progression and cervical parameters

Cervical radiographs were taken at the radiology department of a single institution in a standardized manner. From lateral radiographs, the levels affected and subtype of OPLL involvement was determined [ 1 ]. The transverse thickness (anteroposterior diameter) of OPLL at each cervical level was measured on neutral (i.e. not flexion or extension view) lateral cervical X-rays by drawing a line from the midpoint of the anterior border of the vertebra to the midpoint of the posterior border of the vertebra, and by extending this line to the posterior-most extent of OPLL visible radiologically, for every affected cervical vertebral level (Fig.  2 ). Specifically, the transverse thickness of OPLL at the affected level was the distance from the midpoint of the posterior vertebral border to the posterior-most extent of OPLL visible radiologically. OPLL sagittal length was measured from its cranial border to its caudal-most extent. The corresponding mid-sagittal diameter of the spinal canal posterior to the OPLL was measured from pre-op MRI scans. Measurements at 2-year and 5-year post-op as well as latest follow-up was compared with X-rays taken immediately after the operation. OPLL progression was defined as an increase in transverse thickness or length by ≥ 2 mm in accordance with previous studies [ 1 , 3 , 4 , 22 , 23 , 24 ]. Progression rate was calculated by measuring the difference between the transverse thickness or length of the OPLL following a defined post-operative period and dividing by the duration between radiographs. Cervical sagittal alignment was measured on neutral lateral X-rays between the inferior endplate of C2 and the inferior endplate of C7. If the inferior endplate of C7 was not well visualised, the inferior endplate of C6 was referenced instead. mJOA scores were retrieved from either electronic / physical doctor notes or occupational therapy reports at both the immediate pre-op period as well as upon post-op follow-up.

Radiological measurement of OPLL progression. Lateral cervical X-rays demonstrating the measurement of transverse (red; at C3 level) and longitudinal (blue) extent of OPLL immediately post-op and that taken at latest follow-up in representative cases with and without radiological progression. Panels A and B illustrate a case of progression, whilst panels C and D illustrate a case of non-progression after more than 5 years of follow-up

Statistical analysis

Analysis of variance (ANOVA) was utilised to compare the progression rates at different cervical levels and at different time points from surgery. The intraclass correlation coefficient was calculated from transverse and longitudinal OPLL measurements taken by two observers to assess inter-observer reliability. To compare the progression rate of individual cervical levels, independent t-tests were conducted with a Bonferroni correction applied to account for multiple comparisons. Paired t-test was utilized to analyse the difference between the annual progression rate of the first two years after the operation with that of the subsequent period, in patients with assessment at three or more years after surgery. Chi squared testing was utilized to compare categorical variables. Reported numbers represent mean ± standard deviation unless otherwise stated. Statistical analyses were conducted using SPSS (version 27.0, IBM, Armonk, New York, USA).

Demographic and post-operative details of study cohort

A total of 29 patients consisting of 19 males and 10 females were recruited for analysis. The demographics of subjects with and without transverse OPLL progression are shown in Table  1 . The average age at operation was 61.3 ± 6.7 years old (range of 48–76). Body mass index at the time of operation was 25.0 ± 3.2. A total of 24 of 29 patients had X-rays available at exactly 24-months after the operation, whilst 18 of 29 patients had X-rays at 5-years or more after the operation. 18 patients were classified as having severe DCM (mJOA < 12) according to the preoperative mJOA scores, whilst the remaining 11 patients had moderate DCM (mJOA = 12–14). In 20 of the patients receiving laminoplasty, the hinge was held open by plates, whilst sutures were utilized in the remaining 9 cases. The mean number of cervical levels receiving laminoplasty was 4.2 ± 0.5 (range, 3–5). Patients most often received four-level laminoplasties (C3-C6, 21 patients) and five-level laminoplasties (C3-C7, 7 patients).

Prevalence of OPLL by cervical level and type

Radiological assessment by OPLL by subtype revealed that 17 were continuous, two were segmental, seven were mixed type (continuous and segmental) and three were localised. The mean number of cervical levels with OPLL involvement was 4.1 ± 1.3 (range, 2–7). The AP diameter of OPLL at the thickest affected region was 4.00 ± 1.59 mm. The cervical levels affected by OPLL are summarized in Table  2 , with C4 (29/29 patients), C3 (26/29) and C5 (23/29) levels most often involved. The mean transverse diameters upon immediate post-operative X-rays demonstrated that OPLL was thickest at C3, followed by C4 and C2. Sagittal dimensions of the spinal canal posterior to the OPLL were narrowest over C3, followed by C4, and C5, at 6.63 ± 1.63 mm, 6.70 ± 1.59 mm, and 7.27 ± 1.46 mm respectively.

Overall OPLL progression

Amongst the entire cohort, 79% (23/29) of patients demonstrated at least 2 mm of transverse or longitudinal progression of OPLL at latest follow up. At 2-years and 5-years post-op, these corresponded to 54% (13/24) and 71% (10/14) of the cohort (Table  3 ).

Transverse OPLL progression

The prevalence of transverse OPLL progression at latest follow-up was 45% (13/29). Mean transverse progression rate at latest follow-up regardless of cervical level was 0.14 ± 0.23 mm / year (range 0–1.34 mm). The mean transverse progression rate in the first two years after the operation was compared to the mean transverse progression rate in subsequent years (4.8 ± 2.7 years; range 1.0–10.7). Transverse progression rate in the first two years after laminoplasty was 0.20 ± 0.48 mm/year (range 0–3.40), while that in the subsequent 4.8 years this fell slightly ( p  = 0.643) to 0.17 ± 0.36 mm/year (range 0–2.01).

With regards to cervical level, C5 demonstrated the greatest transverse progression rate at latest follow-up (0.24 ± 0.34 mm/year) followed by the C4 level (0.21 ± 0.28 mm/year). When comparing the transverse progression rate of each cervical level, statistically significant differences were found in comparison of C4, C5 and C6 with C7 ( p  < 0.01). Averaged rates of transverse progression at 2-year, 5-years, and latest follow-up for each cervical level are illustrated in Fig.  3 . The intraclass correlation coefficient for inter-observer measurements of transverse OPLL dimensions upon lateral cervical X-rays was 0.826 (95% CI: 0.789–0.856).

Transverse OPLL progression by cervical level. Average transverse OPLL progression (mm/year) at different cervical levels, by comparing the initial post-operative X-ray to the X-ray taken at 2-year, 5-year and the latest follow-up of each patient. The error bars represent the standard errors of the mean

Longitudinal OPLL progression

69% (20/29) of patients demonstrated longitudinal progression upon their latest X-rays. This corresponded to 50% (12/24) and 71% (10/14) of patients at 2-year and 5-year post-op respectively. The mean longitudinal progression rate at latest follow-up was 1.61 ± 2.06 mm / year (range 0–8.64). The annual longitudinal progression rate in the first two years after the operation was compared to the annual longitudinal progression rate in subsequent years (4.8 ± 2.7 years; range 1.0–10.7) in 17 patients. The annual longitudinal progression rate in the first two years was 2.19 ± 2.75 mm / year (range 0–8.38) decreased to 1.05 ± 1.29 mm / year (range 0–4.96) in the subsequent period which was statistically significant ( p  = 0.042). The intraclass correlation coefficient for inter-observer measurements of sagittal OPLL dimensions upon lateral cervical X-rays was 0.754 (95% CI: 0.617–0.847).

Sagittal alignment

Before the operation, 22 patients were K-line positive, while 7 were K-line negative. Patients with a negative K-line prior to operation demonstrated a lordotic alignment upon extension films. As of the most recent radiological assessment, 16 patients were K-line positive and 13 were K-line negative. The mean pre-operative cervical sagittal alignment was 9.1 ± 9.0 o of lordosis as compared to 4.1 ± 8.3 o at latest follow-up which was a statistically significant decrease ( p  < 0.001).

Complications and neurological survivorship

One patient was noted to have deterioration in left side motor power immediate post-operation but demonstrated spontaneous neurological improvement. He also received debridement for wound infection at 2-weeks post-op. Amongst the overall cohort, preop mJOA was 9.13 ± 3.66 compared to 13.21 ± 2.34 upon peak post-op recovery ( p  < 0.01). The overall mean improvement in mJOA after laminoplasty was 4.33 ± 3.51, and the neurological recovery rate (NRR) was 53.9 ± 28.6%. The mean mJOA increment of patients with transverse progression was 4.33 ± 5.39, while that of those without transverse progression was 4.33 ± 3.11 ( p  = 1.000). No patients required re-operation for neurological deterioration at latest follow-up.

This study examined the progression rate of cervical OPLL following laminoplasty. Our results showed that longitudinal progression occurred more frequently than transverse progression. Reassuringly, none of the patients required revision surgery for neurological deterioration after an average follow-up period exceeding 6-years. To the best of our knowledge, this work represents the first attempt to characterize OPLL progression rate by cervical level affected. Our results are of relevance to surgical planning and patient counselling.

A recent systematic review revealed that cervical laminectomy and fusion resulted in an OPLL progression rate of only 22.7% as compared to 68.8% following cervical laminoplasty [ 25 ], whilst offering similar neurological outcomes [ 23 , 24 , 26 , 27 , 28 , 29 ]. Our results were consistent with this trend, yet laminoplasties remain as a good treatment option in patients with OPLL and a favourable cervical alignment given the absence of neurological deterioration upon mid-term follow-up. Our findings on greatest OPLL progression and canal narrowing at C3-C5 has ramifications on both the execution of laminoplasties, as well as the choice of surgical technique, particularly in a younger patient population. Laminoplasties should be performed with greater hinge opening at these at-risk levels and care to preserve and repair the soft tissues to facilitate greater float back. The opened lamina hinge must be secured with a technique that prevents ‘spring back’, which is common when sutures are used. With regards to choice of surgical technique, younger and fitter patients with sizeable OPLL at C3- C5 and marginal clearance of the K-line would benefit more from direct anterior decompression or posterior instrumented fusion, in view of anticipated radiological progression and associated risk of neurological decline over the long-term. Nevertheless, it remains essential that evidence for post-laminoplasty neurological deterioration due to accelerated OPLL progression at C3-5 is substantiated upon longer follow-up duration.

Our findings for overall progression at 2-years following laminoplasty (54%) corresponded to the literature, which ranged from 38.5 to 56.5% within a similar observational period [ 3 , 30 ]. Similarly, our reported prevalence of progression at 5-years post-op (71%) was comparable to published studies reporting a progression rate of 50–75% [ 22 , 31 , 32 ]. Cervical laminoplasty is a motion-sparing surgery and retention of intervertebral motion has been attributed as a biomechanical factor causing OPLL progression [ 33 ]. The preponderance for OPLL development [ 1 ] and progression at C4 and C5 may be attributed to the relatively greater range of motion at this region compared to the rest of the subaxial cervical spine. Specifically, the flexion and extension range of C4/5 and C5/6 has been documented respectively to be 16–23 o and 15–28 o [ 34 , 35 , 36 , 37 ]. Our findings also revealed that longitudinal OPLL progression was more prevalent than transverse progression. Mean longitudinal progression rate (1.61 mm/year) was compatible to the range documented in prior studies (0.7 to 2.7 mm/year) [ 14 , 24 , 38 , 39 ]. Upon further characterization with interval CTs, longitudinal progression may indicate a need for prophylactic decompression of cervical levels with relative stenosis that are yet to be affected by OPLL.

mJOA scoring is widely considered the gold standard to assess for DCM severity and post-operative recovery rates and exhibits high inter-rater reliability [ 40 ]. Reassuringly, recovery trajectories as evidenced by ΔmJOA was unaffected by OPLL progression. Whilst these findings indicate the general effectiveness of cervical laminoplasty, a caveat concerned the modest cohort size which may have resulted in statistical tests being underpowered, precluding subgroup analysis of neurological outcomes by OPLL subtyping, and by myelopathy severity, as most patients possessed mJOA scores between ‘moderate’ and ‘severe’ thresholds.

Limitations

One of the main limitations of this study was that measurements were based on X-rays alone. Accuracy of the measurements could be affected by the quality and the projection of radiographs as well as the degree of calcification. Nevertheless, we demonstrated substantial agreement in the intra-class correlation coefficient between readers. CT scans were not routinely ordered for post-operative monitoring yet would have offered superior accuracy in determining OPLL dimensions. Post-operative outcomes would have been more comprehensive upon a longer duration of observation, especially for axial progression and recurrence of cord compression, and with the addition of patient-reported outcome measures [ 41 ]. Last but not least, a larger cohort size would be essential to further delineate the relationship between radiological progression of cervical OPLL and neurological recovery, and to allow for subgroup analysis. Whilst our study highlights post-operative radiological OPLL progression, the necessity for studies on population-wide OPLL detection followed by surveillance may be essential for East Asian locales where this disease entity is prevalent [ 42 ] and is tragically often only diagnosed following traumatic spinal cord injury.

Despite radiological progression following laminoplasty, neurological outcomes and survivorship was excellent within the observation period. The rate of progression was greater longitudinally than transversely. Transverse progression of C5 OPLL was highest in comparison to other cervical levels. Our findings are of relevance to the selection of surgical procedure and execution of laminoplasties to minimize the risk of future cervical cord compression. Follow-up studies should be supplemented with larger patient numbers, longer follow-up duration and serial CT/MRI evaluation.

Data availability

No datasets were generated or analysed during the current study.

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Wai Kiu Thomas Liu, Keira Ho Yuet Siu, Jason Pui-Yin Cheung & Graham Ka-Hon Shea

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TWKL: data collection, data analysis, drafting of manuscript. KHYS: data collection, data analysis. JPYC: review of manuscript. GKHS: conception of study, drafting of manuscript. All authors reviewed the manuscript.

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Liu, W.K.T., Yuet Siu, K.H., Cheung, J.PY. et al. Radiographic characterization of OPLL progression in patients receiving laminoplasty with a minimum of two-years follow-up. Neurosurg Rev 47 , 505 (2024). https://doi.org/10.1007/s10143-024-02735-z

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Received : 29 July 2024

Revised : 20 August 2024

Accepted : 22 August 2024

Published : 29 August 2024

DOI : https://doi.org/10.1007/s10143-024-02735-z

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