The effect of chronic caffeine supplementation on endurance performance has been studied extensively in different populations. However, concurrent research on the effects of acute supplementation of caffeine on cardiorespiratory responses during endurance exercise in hot and humid conditions is unavailable
Source: Ping, WC, Keong, CC & Bandyopadhyay, A 2010, ‘Effects of acute supplementation of caffeine on cardiorespiratory responses during endurance running in a hot and humid climate’, Indian Journal of Medical Research, vol. 132, pp. 36–41. Used under a CC-BY-NC-SA licence.
Step two of writing a literature review is synthesis.
Synthesis describes combining separate components or elements to form a connected whole.
You will use the results of your analysis to find themes to build your literature review around. Each of the themes identified will become a subheading within the body of your literature review.
A good place to start when identifying themes is with the dependent variables (results/findings) that were investigated in the research studies.
Because all of the research articles you are incorporating into your literature review are related to your topic, it is likely that they have similar study designs and have measured similar dependent variables. Review the ‘Results’ column of your analysis grid. You may like to collate the common themes in a synthesis grid (see, for example Table 7.4 ).
Step three of writing a literature review is evaluation, which can only be done after carefully analysing your research papers and synthesising the common themes (findings).
During the evaluation stage, you are making judgements on the themes presented in the research articles that you have read. This includes providing physiological explanations for the findings. It may be useful to refer to the discussion section of published original investigation research papers, or another literature review, where the authors may mention tested or hypothetical physiological mechanisms that may explain their findings.
When the findings of the investigations related to a particular theme are inconsistent (e.g., one study shows that caffeine effects performance and another study shows that caffeine had no effect on performance) you should attempt to provide explanations of why the results differ, including physiological explanations. A good place to start is by comparing the methodologies to determine if there are any differences that may explain the differences in the findings (see the ‘Experimental design’ column of your analysis grid). An example of evaluation is shown in the examples that follow in this section, under ‘Running performance’ and ‘RPE ratings’.
When the findings of the papers related to a particular theme are consistent (e.g., caffeine had no effect on oxygen uptake in both studies) an evaluation should include an explanation of why the results are similar. Once again, include physiological explanations. It is still a good idea to compare methodologies as a background to the evaluation. An example of evaluation is shown in the following under ‘Oxygen consumption’.
Once you have completed the analysis, and synthesis grids and written your evaluation of the research papers , you can combine synthesis and evaluation information to create a paragraph for a literature review ( Figure 7.4 ).
The following paragraphs are an example of combining the outcome of the synthesis and evaluation stages to produce a paragraph for a literature review.
Note that this is an example using only two papers – most literature reviews would be presenting information on many more papers than this ( (e.g., 106 papers in the review article by Bain and colleagues discussed later in this chapter). However, the same principle applies regardless of the number of papers reviewed.
The next part of this chapter looks at the each section of a literature review and explains how to write them by referring to a review article that was published in Frontiers in Physiology and shown in Figure 7.1. Each section from the published article is annotated to highlight important features of the format of the review article, and identifies the synthesis and evaluation information.
In the examination of each review article section we will point out examples of how the authors have presented certain information and where they display application of important cognitive processes; we will use the colour code shown below:
This should be one paragraph that accurately reflects the contents of the review article.
The introduction should establish the context and importance of the review
The reference section provides a list of the references that you cited in the body of your review article. The format will depend on the journal of publication as each journal has their own specific referencing format.
It is important to accurately cite references in research papers to acknowledge your sources and ensure credit is appropriately given to authors of work you have referred to. An accurate and comprehensive reference list also shows your readers that you are well-read in your topic area and are aware of the key papers that provide the context to your research.
It is important to keep track of your resources and to reference them consistently in the format required by the publication in which your work will appear. Most scientists will use reference management software to store details of all of the journal articles (and other sources) they use while writing their review article. This software also automates the process of adding in-text references and creating a reference list. In the review article by Bain et al. (2014) used as an example in this chapter, the reference list contains 106 items, so you can imagine how much help referencing software would be. Chapter 5 shows you how to use EndNote, one example of reference management software.
Click the drop down below to review the terms learned from this chapter.
Copyright note:
Bain, A.R., Morrison, S.A., & Ainslie, P.N. (2014). Cerebral oxygenation and hyperthermia. Frontiers in Physiology, 5 , 92.
Pautasso, M. (2013). Ten simple rules for writing a literature review. PLoS Computational Biology, 9 (7), e1003149.
How To Do Science Copyright © 2022 by University of Southern Queensland is licensed under a Creative Commons Attribution-NonCommercial-ShareAlike 4.0 International License , except where otherwise noted.
A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.
Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.
A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:
Given this, the purpose of a literature review is to:
Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.
Types of Literature Reviews
It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.
In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.
Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].
Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.
Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.
Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.
Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.
Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.
NOTE: Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.
Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews." Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.
I. Thinking About Your Literature Review
The structure of a literature review should include the following in support of understanding the research problem :
The critical evaluation of each work should consider :
II. Development of the Literature Review
Four Basic Stages of Writing 1. Problem formulation -- which topic or field is being examined and what are its component issues? 2. Literature search -- finding materials relevant to the subject being explored. 3. Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4. Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.
Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1. Roughly how many sources would be appropriate to include? 2. What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3. Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4. Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5. Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.
III. Ways to Organize Your Literature Review
Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.
Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.
Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:
IV. Writing Your Literature Review
Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.
Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.
V. Common Mistakes to Avoid
These are the most common mistakes made in reviewing social science research literature.
Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.
Break Out of Your Disciplinary Box!
Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.
Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.
Don't Just Review for Content!
While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:
When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.
Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.
When Do I Know I Can Stop Looking and Move On?
Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:
Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.
Joanna Wilkinson
This is our ultimate guide on how to write a narrative literature review. It forms part of our Research Smarter series .
Researchers worldwide are increasingly reliant on literature reviews. That’s because review articles provide you with a broad picture of the field, and help to synthesize published research that’s expanding at a rapid pace .
In some academic fields, researchers publish more literature reviews than original research papers. The graph below shows the substantial growth of narrative literature reviews in the Web of Science™, alongside the percentage increase of reviews when compared to all document types.
It’s critical that researchers across all career levels understand how to produce an objective, critical summary of published research. This is no easy feat, but a necessary one. Professionally constructed literature reviews – whether written by a student in class or an experienced researcher for publication – should aim to add to the literature rather than detract from it.
To help you write a narrative literature review, we’ve put together some top tips in this blog post.
Best practice tips to write a narrative literature review:
We’ll also provide an overview of all the products helpful for your next narrative review, including the Web of Science, EndNote™ and Journal Citation Reports™.
Once you’ve settled on your research question, coming up with a good set of keywords to find papers on your topic can be daunting. This isn’t surprising. Put simply, if you fail to include a relevant paper when you write a narrative literature review, the omission will probably get picked up by your professor or peer reviewers. The end result will likely be a low mark or an unpublished manuscript, neither of which will do justice to your many months of hard work.
Research databases and search engines are an integral part of any literature search. It’s important you utilize as many options available through your library as possible. This will help you search an entire discipline (as well as across disciplines) for a thorough narrative review.
We provide a short summary of the various databases and search engines in an earlier Research Smarter blog . These include the Web of Science , Science.gov and the Directory of Open Access Journals (DOAJ).
Like what you see? Share it with others on Twitter:
[bctt tweet=”Writing a #LiteratureReview? Check out the latest @clarivateAG blog for top tips (from topic searches to working with coauthors), examples, templates and more”]
The Web of Science is a multidisciplinary research engine that contains over 170 million papers from more than 250 academic disciplines. All of the papers in the database are interconnected via citations. That means once you get started with your keyword search, you can follow the trail of cited and citing papers to efficiently find all the relevant literature. This is a great way to ensure you’re not missing anything important when you write a narrative literature review.
We recommend starting your search in the Web of Science Core Collection™. This database covers more than 21,000 carefully selected journals. It is a trusted source to find research papers, and discover top authors and journals (read more about its coverage here ).
Learn more about exploring the Core Collection in our blog, How to find research papers: five tips every researcher should know . Our blog covers various tips, including how to:
Try our tips on the Web of Science now.
As you explore the Web of Science, you may notice that certain papers are marked as “Highly Cited.” These papers can play a significant role when you write a narrative literature review.
Highly Cited papers are recently published papers getting the most attention in your field right now. They form the top 1% of papers based on the number of citations received, compared to other papers published in the same field in the same year.
You will want to identify Highly Cited research as a group of papers. This group will help guide your analysis of the future of the field and opportunities for future research. This is an important component of your conclusion.
Writing reviews is hard work…[it] not only organizes published papers, but also positions t hem in the academic process and presents the future direction. Prof. Susumu Kitagawa, Highly Cited Researcher, Kyoto University
Writing a narrative review on your own is hard, but it can be even more challenging if you’re collaborating with a team, especially if your coauthors are working across multiple locations. Luckily, reference management software can improve the coordination between you and your co-authors—both around the department and around the world.
We’ve written about how to use EndNote’s Cite While You Write feature, which will help you save hundreds of hours when writing research . Here, we discuss the features that give you greater ease and control when collaborating with your colleagues.
Sharing references is essential for successful collaboration. With EndNote, you can store and share as many references, documents and files as you need with up to 100 people using the software.
You can share simultaneous access to one reference library, regardless of your colleague’s location or organization. You can also choose the type of access each user has on an individual basis. For example, Read-Write access means a select colleague can add and delete references, annotate PDF articles and create custom groups. They’ll also be able to see up to 500 of the team’s most recent changes to the reference library. Read-only is also an option for individuals who don’t need that level of access.
EndNote helps you overcome research limitations by synchronizing library changes every 15 minutes. That means your team can stay up-to-date at any time of the day, supporting an easier, more successful collaboration.
Start your free EndNote trial today .
Finding the right journal for your literature review can be a particular pain point for those of you who want to publish. The expansion of scholarly journals has made the task extremely difficult, and can potentially delay the publication of your work by many months.
We’ve written a blog about how you can find the right journal for your manuscript using a rich array of data. You can read our blog here , or head straight to Endnote’s Manuscript Matcher or Journal Citation Report s to try out the best tools for the job.
There are a few tips we haven’t covered in this blog, including how to decide on an area of research, develop an interesting storyline, and highlight gaps in the literature. We’ve listed a few blogs here that might help you with this, alongside some literature review examples and outlines to get you started.
Literature Review examples:
(Make sure you download the free EndNote™ Click browser plugin to access the full-text PDFs).
Templates and outlines:
Additional resources:
Unlocking emerging topics in research with research horizon navigator.
Nowadays, there is a huge demand for scientific literature reviews as they are especially appreciated by scholars or researchers when designing their research proposals. While finding information is less of a problem to them, discerning which paper or publication has enough quality has become one of the biggest issues. Literature reviews narrow the current knowledge on a certain field and examine the latest publications’ strengths and weaknesses. This way, they are priceless tools not only for those who are starting their research, but also for all those interested in recent publications. To be useful, literature reviews must be written in a professional way with a clear structure. The amount of work needed to write a scientific literature review must be considered before starting one since the tasks required can overwhelm many if the working method is not the best.
Writing a scientific review implies both researching for relevant academic content and writing , however, writing without having a clear objective is a common mistake. Sometimes, studying the situation and defining the work’s system is so important and takes equally as much time as that required in writing the final result. Therefore, we suggest that you divide your path into three steps.
Think about your target and narrow down your topic. If you don’t choose a well-defined topic, you can find yourself dealing with a wide subject and plenty of publications about it. Remember that researchers usually deal with really specific fields of study.
It is time to be a critic and locate only pertinent publications. While researching for content consider publications that were written 3 years ago at the most. Write notes and summarize the content of each paper as that will help you in the next step.
Check some literature review examples to decide how to start writing a good literature review . When your goals and structure are defined, begin writing without forgetting your target at any moment.
Related: Conducting a literature survey? Wish to learn more about scientific misconduct? Check out this resourceful infographic.
Here you have a to-do list to help you write your review :
Scholars and researchers are usually the best candidates to write scientific literature reviews, not only because they are experts in a certain field, but also because they know the exigencies and needs that researchers have while writing research proposals or looking for information among thousands of academic papers. Therefore, considering your experience as a researcher can help you understand how to write a scientific literature review.
Have you faced challenges while drafting your first literature review? How do you think can these tips help you in acing your next literature review? Let us know in the comments section below! You can also visit our Q&A forum for frequently asked questions related to copyrights answered by our team that comprises eminent researchers and publication experts.
Thank you for your information. It adds knowledge on critical review being a first time to do it, it helps a lot.
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Jacalyn kelly.
1 Clinical Biochemistry, Department of Pediatric Laboratory Medicine, The Hospital for Sick Children, University of Toronto, Toronto, Ontario, Canada
Khosrow adeli.
2 Department of Laboratory Medicine and Pathobiology, University of Toronto, Toronto, Canada
3 Chair, Communications and Publications Division (CPD), International Federation for Sick Clinical Chemistry (IFCC), Milan, Italy
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Peer review has been defined as a process of subjecting an author’s scholarly work, research or ideas to the scrutiny of others who are experts in the same field. It functions to encourage authors to meet the accepted high standards of their discipline and to control the dissemination of research data to ensure that unwarranted claims, unacceptable interpretations or personal views are not published without prior expert review. Despite its wide-spread use by most journals, the peer review process has also been widely criticised due to the slowness of the process to publish new findings and due to perceived bias by the editors and/or reviewers. Within the scientific community, peer review has become an essential component of the academic writing process. It helps ensure that papers published in scientific journals answer meaningful research questions and draw accurate conclusions based on professionally executed experimentation. Submission of low quality manuscripts has become increasingly prevalent, and peer review acts as a filter to prevent this work from reaching the scientific community. The major advantage of a peer review process is that peer-reviewed articles provide a trusted form of scientific communication. Since scientific knowledge is cumulative and builds on itself, this trust is particularly important. Despite the positive impacts of peer review, critics argue that the peer review process stifles innovation in experimentation, and acts as a poor screen against plagiarism. Despite its downfalls, there has not yet been a foolproof system developed to take the place of peer review, however, researchers have been looking into electronic means of improving the peer review process. Unfortunately, the recent explosion in online only/electronic journals has led to mass publication of a large number of scientific articles with little or no peer review. This poses significant risk to advances in scientific knowledge and its future potential. The current article summarizes the peer review process, highlights the pros and cons associated with different types of peer review, and describes new methods for improving peer review.
Peer Review is defined as “a process of subjecting an author’s scholarly work, research or ideas to the scrutiny of others who are experts in the same field” ( 1 ). Peer review is intended to serve two primary purposes. Firstly, it acts as a filter to ensure that only high quality research is published, especially in reputable journals, by determining the validity, significance and originality of the study. Secondly, peer review is intended to improve the quality of manuscripts that are deemed suitable for publication. Peer reviewers provide suggestions to authors on how to improve the quality of their manuscripts, and also identify any errors that need correcting before publication.
The concept of peer review was developed long before the scholarly journal. In fact, the peer review process is thought to have been used as a method of evaluating written work since ancient Greece ( 2 ). The peer review process was first described by a physician named Ishaq bin Ali al-Rahwi of Syria, who lived from 854-931 CE, in his book Ethics of the Physician ( 2 ). There, he stated that physicians must take notes describing the state of their patients’ medical conditions upon each visit. Following treatment, the notes were scrutinized by a local medical council to determine whether the physician had met the required standards of medical care. If the medical council deemed that the appropriate standards were not met, the physician in question could receive a lawsuit from the maltreated patient ( 2 ).
The invention of the printing press in 1453 allowed written documents to be distributed to the general public ( 3 ). At this time, it became more important to regulate the quality of the written material that became publicly available, and editing by peers increased in prevalence. In 1620, Francis Bacon wrote the work Novum Organum, where he described what eventually became known as the first universal method for generating and assessing new science ( 3 ). His work was instrumental in shaping the Scientific Method ( 3 ). In 1665, the French Journal des sçavans and the English Philosophical Transactions of the Royal Society were the first scientific journals to systematically publish research results ( 4 ). Philosophical Transactions of the Royal Society is thought to be the first journal to formalize the peer review process in 1665 ( 5 ), however, it is important to note that peer review was initially introduced to help editors decide which manuscripts to publish in their journals, and at that time it did not serve to ensure the validity of the research ( 6 ). It did not take long for the peer review process to evolve, and shortly thereafter papers were distributed to reviewers with the intent of authenticating the integrity of the research study before publication. The Royal Society of Edinburgh adhered to the following peer review process, published in their Medical Essays and Observations in 1731: “Memoirs sent by correspondence are distributed according to the subject matter to those members who are most versed in these matters. The report of their identity is not known to the author.” ( 7 ). The Royal Society of London adopted this review procedure in 1752 and developed the “Committee on Papers” to review manuscripts before they were published in Philosophical Transactions ( 6 ).
Peer review in the systematized and institutionalized form has developed immensely since the Second World War, at least partly due to the large increase in scientific research during this period ( 7 ). It is now used not only to ensure that a scientific manuscript is experimentally and ethically sound, but also to determine which papers sufficiently meet the journal’s standards of quality and originality before publication. Peer review is now standard practice by most credible scientific journals, and is an essential part of determining the credibility and quality of work submitted.
Peer review has become the foundation of the scholarly publication system because it effectively subjects an author’s work to the scrutiny of other experts in the field. Thus, it encourages authors to strive to produce high quality research that will advance the field. Peer review also supports and maintains integrity and authenticity in the advancement of science. A scientific hypothesis or statement is generally not accepted by the academic community unless it has been published in a peer-reviewed journal ( 8 ). The Institute for Scientific Information ( ISI ) only considers journals that are peer-reviewed as candidates to receive Impact Factors. Peer review is a well-established process which has been a formal part of scientific communication for over 300 years.
The peer review process begins when a scientist completes a research study and writes a manuscript that describes the purpose, experimental design, results, and conclusions of the study. The scientist then submits this paper to a suitable journal that specializes in a relevant research field, a step referred to as pre-submission. The editors of the journal will review the paper to ensure that the subject matter is in line with that of the journal, and that it fits with the editorial platform. Very few papers pass this initial evaluation. If the journal editors feel the paper sufficiently meets these requirements and is written by a credible source, they will send the paper to accomplished researchers in the field for a formal peer review. Peer reviewers are also known as referees (this process is summarized in Figure 1 ). The role of the editor is to select the most appropriate manuscripts for the journal, and to implement and monitor the peer review process. Editors must ensure that peer reviews are conducted fairly, and in an effective and timely manner. They must also ensure that there are no conflicts of interest involved in the peer review process.
Overview of the review process
When a reviewer is provided with a paper, he or she reads it carefully and scrutinizes it to evaluate the validity of the science, the quality of the experimental design, and the appropriateness of the methods used. The reviewer also assesses the significance of the research, and judges whether the work will contribute to advancement in the field by evaluating the importance of the findings, and determining the originality of the research. Additionally, reviewers identify any scientific errors and references that are missing or incorrect. Peer reviewers give recommendations to the editor regarding whether the paper should be accepted, rejected, or improved before publication in the journal. The editor will mediate author-referee discussion in order to clarify the priority of certain referee requests, suggest areas that can be strengthened, and overrule reviewer recommendations that are beyond the study’s scope ( 9 ). If the paper is accepted, as per suggestion by the peer reviewer, the paper goes into the production stage, where it is tweaked and formatted by the editors, and finally published in the scientific journal. An overview of the review process is presented in Figure 1 .
Peer reviews are conducted by scientific experts with specialized knowledge on the content of the manuscript, as well as by scientists with a more general knowledge base. Peer reviewers can be anyone who has competence and expertise in the subject areas that the journal covers. Reviewers can range from young and up-and-coming researchers to old masters in the field. Often, the young reviewers are the most responsive and deliver the best quality reviews, though this is not always the case. On average, a reviewer will conduct approximately eight reviews per year, according to a study on peer review by the Publishing Research Consortium (PRC) ( 7 ). Journals will often have a pool of reviewers with diverse backgrounds to allow for many different perspectives. They will also keep a rather large reviewer bank, so that reviewers do not get burnt out, overwhelmed or time constrained from reviewing multiple articles simultaneously.
Referees are typically not paid to conduct peer reviews and the process takes considerable effort, so the question is raised as to what incentive referees have to review at all. Some feel an academic duty to perform reviews, and are of the mentality that if their peers are expected to review their papers, then they should review the work of their peers as well. Reviewers may also have personal contacts with editors, and may want to assist as much as possible. Others review to keep up-to-date with the latest developments in their field, and reading new scientific papers is an effective way to do so. Some scientists use peer review as an opportunity to advance their own research as it stimulates new ideas and allows them to read about new experimental techniques. Other reviewers are keen on building associations with prestigious journals and editors and becoming part of their community, as sometimes reviewers who show dedication to the journal are later hired as editors. Some scientists see peer review as a chance to become aware of the latest research before their peers, and thus be first to develop new insights from the material. Finally, in terms of career development, peer reviewing can be desirable as it is often noted on one’s resume or CV. Many institutions consider a researcher’s involvement in peer review when assessing their performance for promotions ( 11 ). Peer reviewing can also be an effective way for a scientist to show their superiors that they are committed to their scientific field ( 5 ).
A 2009 international survey of 4000 peer reviewers conducted by the charity Sense About Science at the British Science Festival at the University of Surrey, found that 90% of reviewers were keen to peer review ( 12 ). One third of respondents to the survey said they were happy to review up to five papers per year, and an additional one third of respondents were happy to review up to ten.
On average, it takes approximately six hours to review one paper ( 12 ), however, this number may vary greatly depending on the content of the paper and the nature of the peer reviewer. One in every 100 participants in the “Sense About Science” survey claims to have taken more than 100 hours to review their last paper ( 12 ).
Ulrichsweb is a directory that provides information on over 300,000 periodicals, including information regarding which journals are peer reviewed ( 13 ). After logging into the system using an institutional login (eg. from the University of Toronto), search terms, journal titles or ISSN numbers can be entered into the search bar. The database provides the title, publisher, and country of origin of the journal, and indicates whether the journal is still actively publishing. The black book symbol (labelled ‘refereed’) reveals that the journal is peer reviewed.
As previously mentioned, when a reviewer receives a scientific manuscript, he/she will first determine if the subject matter is well suited for the content of the journal. The reviewer will then consider whether the research question is important and original, a process which may be aided by a literature scan of review articles.
Scientific papers submitted for peer review usually follow a specific structure that begins with the title, followed by the abstract, introduction, methodology, results, discussion, conclusions, and references. The title must be descriptive and include the concept and organism investigated, and potentially the variable manipulated and the systems used in the study. The peer reviewer evaluates if the title is descriptive enough, and ensures that it is clear and concise. A study by the National Association of Realtors (NAR) published by the Oxford University Press in 2006 indicated that the title of a manuscript plays a significant role in determining reader interest, as 72% of respondents said they could usually judge whether an article will be of interest to them based on the title and the author, while 13% of respondents claimed to always be able to do so ( 14 ).
The abstract is a summary of the paper, which briefly mentions the background or purpose, methods, key results, and major conclusions of the study. The peer reviewer assesses whether the abstract is sufficiently informative and if the content of the abstract is consistent with the rest of the paper. The NAR study indicated that 40% of respondents could determine whether an article would be of interest to them based on the abstract alone 60-80% of the time, while 32% could judge an article based on the abstract 80-100% of the time ( 14 ). This demonstrates that the abstract alone is often used to assess the value of an article.
The introduction of a scientific paper presents the research question in the context of what is already known about the topic, in order to identify why the question being studied is of interest to the scientific community, and what gap in knowledge the study aims to fill ( 15 ). The introduction identifies the study’s purpose and scope, briefly describes the general methods of investigation, and outlines the hypothesis and predictions ( 15 ). The peer reviewer determines whether the introduction provides sufficient background information on the research topic, and ensures that the research question and hypothesis are clearly identifiable.
The methods section describes the experimental procedures, and explains why each experiment was conducted. The methods section also includes the equipment and reagents used in the investigation. The methods section should be detailed enough that it can be used it to repeat the experiment ( 15 ). Methods are written in the past tense and in the active voice. The peer reviewer assesses whether the appropriate methods were used to answer the research question, and if they were written with sufficient detail. If information is missing from the methods section, it is the peer reviewer’s job to identify what details need to be added.
The results section is where the outcomes of the experiment and trends in the data are explained without judgement, bias or interpretation ( 15 ). This section can include statistical tests performed on the data, as well as figures and tables in addition to the text. The peer reviewer ensures that the results are described with sufficient detail, and determines their credibility. Reviewers also confirm that the text is consistent with the information presented in tables and figures, and that all figures and tables included are important and relevant ( 15 ). The peer reviewer will also make sure that table and figure captions are appropriate both contextually and in length, and that tables and figures present the data accurately.
The discussion section is where the data is analyzed. Here, the results are interpreted and related to past studies ( 15 ). The discussion describes the meaning and significance of the results in terms of the research question and hypothesis, and states whether the hypothesis was supported or rejected. This section may also provide possible explanations for unusual results and suggestions for future research ( 15 ). The discussion should end with a conclusions section that summarizes the major findings of the investigation. The peer reviewer determines whether the discussion is clear and focused, and whether the conclusions are an appropriate interpretation of the results. Reviewers also ensure that the discussion addresses the limitations of the study, any anomalies in the results, the relationship of the study to previous research, and the theoretical implications and practical applications of the study.
The references are found at the end of the paper, and list all of the information sources cited in the text to describe the background, methods, and/or interpret results. Depending on the citation method used, the references are listed in alphabetical order according to author last name, or numbered according to the order in which they appear in the paper. The peer reviewer ensures that references are used appropriately, cited accurately, formatted correctly, and that none are missing.
Finally, the peer reviewer determines whether the paper is clearly written and if the content seems logical. After thoroughly reading through the entire manuscript, they determine whether it meets the journal’s standards for publication,
and whether it falls within the top 25% of papers in its field ( 16 ) to determine priority for publication. An overview of what a peer reviewer looks for when evaluating a manuscript, in order of importance, is presented in Figure 2 .
How a peer review evaluates a manuscript
To increase the chance of success in the peer review process, the author must ensure that the paper fully complies with the journal guidelines before submission. The author must also be open to criticism and suggested revisions, and learn from mistakes made in previous submissions.
The peer review process is generally conducted in one of three ways: open review, single-blind review, or double-blind review. In an open review, both the author of the paper and the peer reviewer know one another’s identity. Alternatively, in single-blind review, the reviewer’s identity is kept private, but the author’s identity is revealed to the reviewer. In double-blind review, the identities of both the reviewer and author are kept anonymous. Open peer review is advantageous in that it prevents the reviewer from leaving malicious comments, being careless, or procrastinating completion of the review ( 2 ). It encourages reviewers to be open and honest without being disrespectful. Open reviewing also discourages plagiarism amongst authors ( 2 ). On the other hand, open peer review can also prevent reviewers from being honest for fear of developing bad rapport with the author. The reviewer may withhold or tone down their criticisms in order to be polite ( 2 ). This is especially true when younger reviewers are given a more esteemed author’s work, in which case the reviewer may be hesitant to provide criticism for fear that it will damper their relationship with a superior ( 2 ). According to the Sense About Science survey, editors find that completely open reviewing decreases the number of people willing to participate, and leads to reviews of little value ( 12 ). In the aforementioned study by the PRC, only 23% of authors surveyed had experience with open peer review ( 7 ).
Single-blind peer review is by far the most common. In the PRC study, 85% of authors surveyed had experience with single-blind peer review ( 7 ). This method is advantageous as the reviewer is more likely to provide honest feedback when their identity is concealed ( 2 ). This allows the reviewer to make independent decisions without the influence of the author ( 2 ). The main disadvantage of reviewer anonymity, however, is that reviewers who receive manuscripts on subjects similar to their own research may be tempted to delay completing the review in order to publish their own data first ( 2 ).
Double-blind peer review is advantageous as it prevents the reviewer from being biased against the author based on their country of origin or previous work ( 2 ). This allows the paper to be judged based on the quality of the content, rather than the reputation of the author. The Sense About Science survey indicates that 76% of researchers think double-blind peer review is a good idea ( 12 ), and the PRC survey indicates that 45% of authors have had experience with double-blind peer review ( 7 ). The disadvantage of double-blind peer review is that, especially in niche areas of research, it can sometimes be easy for the reviewer to determine the identity of the author based on writing style, subject matter or self-citation, and thus, impart bias ( 2 ).
Masking the author’s identity from peer reviewers, as is the case in double-blind review, is generally thought to minimize bias and maintain review quality. A study by Justice et al. in 1998 investigated whether masking author identity affected the quality of the review ( 17 ). One hundred and eighteen manuscripts were randomized; 26 were peer reviewed as normal, and 92 were moved into the ‘intervention’ arm, where editor quality assessments were completed for 77 manuscripts and author quality assessments were completed for 40 manuscripts ( 17 ). There was no perceived difference in quality between the masked and unmasked reviews. Additionally, the masking itself was often unsuccessful, especially with well-known authors ( 17 ). However, a previous study conducted by McNutt et al. had different results ( 18 ). In this case, blinding was successful 73% of the time, and they found that when author identity was masked, the quality of review was slightly higher ( 18 ). Although Justice et al. argued that this difference was too small to be consequential, their study targeted only biomedical journals, and the results cannot be generalized to journals of a different subject matter ( 17 ). Additionally, there were problems masking the identities of well-known authors, introducing a flaw in the methods. Regardless, Justice et al. concluded that masking author identity from reviewers may not improve review quality ( 17 ).
In addition to open, single-blind and double-blind peer review, there are two experimental forms of peer review. In some cases, following publication, papers may be subjected to post-publication peer review. As many papers are now published online, the scientific community has the opportunity to comment on these papers, engage in online discussions and post a formal review. For example, online publishers PLOS and BioMed Central have enabled scientists to post comments on published papers if they are registered users of the site ( 10 ). Philica is another journal launched with this experimental form of peer review. Only 8% of authors surveyed in the PRC study had experience with post-publication review ( 7 ). Another experimental form of peer review called Dynamic Peer Review has also emerged. Dynamic peer review is conducted on websites such as Naboj, which allow scientists to conduct peer reviews on articles in the preprint media ( 19 ). The peer review is conducted on repositories and is a continuous process, which allows the public to see both the article and the reviews as the article is being developed ( 19 ). Dynamic peer review helps prevent plagiarism as the scientific community will already be familiar with the work before the peer reviewed version appears in print ( 19 ). Dynamic review also reduces the time lag between manuscript submission and publishing. An example of a preprint server is the ‘arXiv’ developed by Paul Ginsparg in 1991, which is used primarily by physicists ( 19 ). These alternative forms of peer review are still un-established and experimental. Traditional peer review is time-tested and still highly utilized. All methods of peer review have their advantages and deficiencies, and all are prone to error.
Open access (OA) journals are becoming increasingly popular as they allow the potential for widespread distribution of publications in a timely manner ( 20 ). Nevertheless, there can be issues regarding the peer review process of open access journals. In a study published in Science in 2013, John Bohannon submitted 304 slightly different versions of a fictional scientific paper (written by a fake author, working out of a non-existent institution) to a selected group of OA journals. This study was performed in order to determine whether papers submitted to OA journals are properly reviewed before publication in comparison to subscription-based journals. The journals in this study were selected from the Directory of Open Access Journals (DOAJ) and Biall’s List, a list of journals which are potentially predatory, and all required a fee for publishing ( 21 ). Of the 304 journals, 157 accepted a fake paper, suggesting that acceptance was based on financial interest rather than the quality of article itself, while 98 journals promptly rejected the fakes ( 21 ). Although this study highlights useful information on the problems associated with lower quality publishers that do not have an effective peer review system in place, the article also generalizes the study results to all OA journals, which can be detrimental to the general perception of OA journals. There were two limitations of the study that made it impossible to accurately determine the relationship between peer review and OA journals: 1) there was no control group (subscription-based journals), and 2) the fake papers were sent to a non-randomized selection of journals, resulting in bias.
Based on a recent survey, the average acceptance rate for papers submitted to scientific journals is about 50% ( 7 ). Twenty percent of the submitted manuscripts that are not accepted are rejected prior to review, and 30% are rejected following review ( 7 ). Of the 50% accepted, 41% are accepted with the condition of revision, while only 9% are accepted without the request for revision ( 7 ).
Based on a recent survey by the PRC, 64% of academics are satisfied with the current system of peer review, and only 12% claimed to be ‘dissatisfied’ ( 7 ). The large majority, 85%, agreed with the statement that ‘scientific communication is greatly helped by peer review’ ( 7 ). There was a similarly high level of support (83%) for the idea that peer review ‘provides control in scientific communication’ ( 7 ).
The following are ten tips on how to be an effective peer reviewer as indicated by Brian Lucey, an expert on the subject ( 22 ):
Peer review is a mutual responsibility among fellow scientists, and scientists are expected, as part of the academic community, to take part in peer review. If one is to expect others to review their work, they should commit to reviewing the work of others as well, and put effort into it.
If the paper is of low quality, suggest that it be rejected, but do not leave ad hominem comments. There is no benefit to being ruthless.
When emailing a scientist to ask them to conduct a peer review, the majority of journals will provide a link to either accept or reject. Do not respond to the email, respond to the link.
Suggest how the authors can overcome the shortcomings in their paper. A review should guide the author on what is good and what needs work from the reviewer’s perspective.
The peer reviewer plays the role of a scientific peer, not an editor for proofreading or decision-making. Don’t fill a review with comments on editorial and typographic issues. Instead, focus on adding value with scientific knowledge and commenting on the credibility of the research conducted and conclusions drawn. If the paper has a lot of typographical errors, suggest that it be professionally proof edited as part of the review.
Stick to the timeline given when conducting a peer review. Editors track who is reviewing what and when and will know if someone is late on completing a review. It is important to be timely both out of respect for the journal and the author, as well as to not develop a reputation of being late for review deadlines.
The peer reviewer must be realistic about the work presented, the changes they suggest and their role. Peer reviewers may set the bar too high for the paper they are editing by proposing changes that are too ambitious and editors must override them.
Ensure that the review is scientific, helpful and courteous. Be sensitive and respectful with word choice and tone in a review.
Remember that both specialists and generalists can provide valuable insight when peer reviewing. Editors will try to get both specialised and general reviewers for any particular paper to allow for different perspectives. If someone is asked to review, the editor has determined they have a valid and useful role to play, even if the paper is not in their area of expertise.
A review requires structure and logical flow. A reviewer should proofread their review before submitting it for structural, grammatical and spelling errors as well as for clarity. Most publishers provide short guides on structuring a peer review on their website. Begin with an overview of the proposed improvements; then provide feedback on the paper structure, the quality of data sources and methods of investigation used, the logical flow of argument, and the validity of conclusions drawn. Then provide feedback on style, voice and lexical concerns, with suggestions on how to improve.
In addition, the American Physiology Society (APS) recommends in its Peer Review 101 Handout that peer reviewers should put themselves in both the editor’s and author’s shoes to ensure that they provide what both the editor and the author need and expect ( 11 ). To please the editor, the reviewer should ensure that the peer review is completed on time, and that it provides clear explanations to back up recommendations. To be helpful to the author, the reviewer must ensure that their feedback is constructive. It is suggested that the reviewer take time to think about the paper; they should read it once, wait at least a day, and then re-read it before writing the review ( 11 ). The APS also suggests that Graduate students and researchers pay attention to how peer reviewers edit their work, as well as to what edits they find helpful, in order to learn how to peer review effectively ( 11 ). Additionally, it is suggested that Graduate students practice reviewing by editing their peers’ papers and asking a faculty member for feedback on their efforts. It is recommended that young scientists offer to peer review as often as possible in order to become skilled at the process ( 11 ). The majority of students, fellows and trainees do not get formal training in peer review, but rather learn by observing their mentors. According to the APS, one acquires experience through networking and referrals, and should therefore try to strengthen relationships with journal editors by offering to review manuscripts ( 11 ). The APS also suggests that experienced reviewers provide constructive feedback to students and junior colleagues on their peer review efforts, and encourages them to peer review to demonstrate the importance of this process in improving science ( 11 ).
The peer reviewer should only comment on areas of the manuscript that they are knowledgeable about ( 23 ). If there is any section of the manuscript they feel they are not qualified to review, they should mention this in their comments and not provide further feedback on that section. The peer reviewer is not permitted to share any part of the manuscript with a colleague (even if they may be more knowledgeable in the subject matter) without first obtaining permission from the editor ( 23 ). If a peer reviewer comes across something they are unsure of in the paper, they can consult the literature to try and gain insight. It is important for scientists to remember that if a paper can be improved by the expertise of one of their colleagues, the journal must be informed of the colleague’s help, and approval must be obtained for their colleague to read the protected document. Additionally, the colleague must be identified in the confidential comments to the editor, in order to ensure that he/she is appropriately credited for any contributions ( 23 ). It is the job of the reviewer to make sure that the colleague assisting is aware of the confidentiality of the peer review process ( 23 ). Once the review is complete, the manuscript must be destroyed and cannot be saved electronically by the reviewers ( 23 ).
When performing a peer review, there are some common scientific errors to look out for. Most of these errors are violations of logic and common sense: these may include contradicting statements, unwarranted conclusions, suggestion of causation when there is only support for correlation, inappropriate extrapolation, circular reasoning, or pursuit of a trivial question ( 24 ). It is also common for authors to suggest that two variables are different because the effects of one variable are statistically significant while the effects of the other variable are not, rather than directly comparing the two variables ( 24 ). Authors sometimes oversee a confounding variable and do not control for it, or forget to include important details on how their experiments were controlled or the physical state of the organisms studied ( 24 ). Another common fault is the author’s failure to define terms or use words with precision, as these practices can mislead readers ( 24 ). Jargon and/or misused terms can be a serious problem in papers. Inaccurate statements about specific citations are also a common occurrence ( 24 ). Additionally, many studies produce knowledge that can be applied to areas of science outside the scope of the original study, therefore it is better for reviewers to look at the novelty of the idea, conclusions, data, and methodology, rather than scrutinize whether or not the paper answered the specific question at hand ( 24 ). Although it is important to recognize these points, when performing a review it is generally better practice for the peer reviewer to not focus on a checklist of things that could be wrong, but rather carefully identify the problems specific to each paper and continuously ask themselves if anything is missing ( 24 ). An extremely detailed description of how to conduct peer review effectively is presented in the paper How I Review an Original Scientific Article written by Frederic G. Hoppin, Jr. It can be accessed through the American Physiological Society website under the Peer Review Resources section.
A major criticism of peer review is that there is little evidence that the process actually works, that it is actually an effective screen for good quality scientific work, and that it actually improves the quality of scientific literature. As a 2002 study published in the Journal of the American Medical Association concluded, ‘Editorial peer review, although widely used, is largely untested and its effects are uncertain’ ( 25 ). Critics also argue that peer review is not effective at detecting errors. Highlighting this point, an experiment by Godlee et al. published in the British Medical Journal (BMJ) inserted eight deliberate errors into a paper that was nearly ready for publication, and then sent the paper to 420 potential reviewers ( 7 ). Of the 420 reviewers that received the paper, 221 (53%) responded, the average number of errors spotted by reviewers was two, no reviewer spotted more than five errors, and 35 reviewers (16%) did not spot any.
Another criticism of peer review is that the process is not conducted thoroughly by scientific conferences with the goal of obtaining large numbers of submitted papers. Such conferences often accept any paper sent in, regardless of its credibility or the prevalence of errors, because the more papers they accept, the more money they can make from author registration fees ( 26 ). This misconduct was exposed in 2014 by three MIT graduate students by the names of Jeremy Stribling, Dan Aguayo and Maxwell Krohn, who developed a simple computer program called SCIgen that generates nonsense papers and presents them as scientific papers ( 26 ). Subsequently, a nonsense SCIgen paper submitted to a conference was promptly accepted. Nature recently reported that French researcher Cyril Labbé discovered that sixteen SCIgen nonsense papers had been used by the German academic publisher Springer ( 26 ). Over 100 nonsense papers generated by SCIgen were published by the US Institute of Electrical and Electronic Engineers (IEEE) ( 26 ). Both organisations have been working to remove the papers. Labbé developed a program to detect SCIgen papers and has made it freely available to ensure publishers and conference organizers do not accept nonsense work in the future. It is available at this link: http://scigendetect.on.imag.fr/main.php ( 26 ).
Additionally, peer review is often criticized for being unable to accurately detect plagiarism. However, many believe that detecting plagiarism cannot practically be included as a component of peer review. As explained by Alice Tuff, development manager at Sense About Science, ‘The vast majority of authors and reviewers think peer review should detect plagiarism (81%) but only a minority (38%) think it is capable. The academic time involved in detecting plagiarism through peer review would cause the system to grind to a halt’ ( 27 ). Publishing house Elsevier began developing electronic plagiarism tools with the help of journal editors in 2009 to help improve this issue ( 27 ).
It has also been argued that peer review has lowered research quality by limiting creativity amongst researchers. Proponents of this view claim that peer review has repressed scientists from pursuing innovative research ideas and bold research questions that have the potential to make major advances and paradigm shifts in the field, as they believe that this work will likely be rejected by their peers upon review ( 28 ). Indeed, in some cases peer review may result in rejection of innovative research, as some studies may not seem particularly strong initially, yet may be capable of yielding very interesting and useful developments when examined under different circumstances, or in the light of new information ( 28 ). Scientists that do not believe in peer review argue that the process stifles the development of ingenious ideas, and thus the release of fresh knowledge and new developments into the scientific community.
Another issue that peer review is criticized for, is that there are a limited number of people that are competent to conduct peer review compared to the vast number of papers that need reviewing. An enormous number of papers published (1.3 million papers in 23,750 journals in 2006), but the number of competent peer reviewers available could not have reviewed them all ( 29 ). Thus, people who lack the required expertise to analyze the quality of a research paper are conducting reviews, and weak papers are being accepted as a result. It is now possible to publish any paper in an obscure journal that claims to be peer-reviewed, though the paper or journal itself could be substandard ( 29 ). On a similar note, the US National Library of Medicine indexes 39 journals that specialize in alternative medicine, and though they all identify themselves as “peer-reviewed”, they rarely publish any high quality research ( 29 ). This highlights the fact that peer review of more controversial or specialized work is typically performed by people who are interested and hold similar views or opinions as the author, which can cause bias in their review. For instance, a paper on homeopathy is likely to be reviewed by fellow practicing homeopaths, and thus is likely to be accepted as credible, though other scientists may find the paper to be nonsense ( 29 ). In some cases, papers are initially published, but their credibility is challenged at a later date and they are subsequently retracted. Retraction Watch is a website dedicated to revealing papers that have been retracted after publishing, potentially due to improper peer review ( 30 ).
Additionally, despite its many positive outcomes, peer review is also criticized for being a delay to the dissemination of new knowledge into the scientific community, and as an unpaid-activity that takes scientists’ time away from activities that they would otherwise prioritize, such as research and teaching, for which they are paid ( 31 ). As described by Eva Amsen, Outreach Director for F1000Research, peer review was originally developed as a means of helping editors choose which papers to publish when journals had to limit the number of papers they could print in one issue ( 32 ). However, nowadays most journals are available online, either exclusively or in addition to print, and many journals have very limited printing runs ( 32 ). Since there are no longer page limits to journals, any good work can and should be published. Consequently, being selective for the purpose of saving space in a journal is no longer a valid excuse that peer reviewers can use to reject a paper ( 32 ). However, some reviewers have used this excuse when they have personal ulterior motives, such as getting their own research published first.
F1000Research was launched in January 2013 by Faculty of 1000 as an open access journal that immediately publishes papers (after an initial check to ensure that the paper is in fact produced by a scientist and has not been plagiarised), and then conducts transparent post-publication peer review ( 32 ). F1000Research aims to prevent delays in new science reaching the academic community that are caused by prolonged publication times ( 32 ). It also aims to make peer reviewing more fair by eliminating any anonymity, which prevents reviewers from delaying the completion of a review so they can publish their own similar work first ( 32 ). F1000Research offers completely open peer review, where everything is published, including the name of the reviewers, their review reports, and the editorial decision letters ( 32 ).
PeerJ was founded by Jason Hoyt and Peter Binfield in June 2012 as an open access, peer reviewed scholarly journal for the Biological and Medical Sciences ( 33 ). PeerJ selects articles to publish based only on scientific and methodological soundness, not on subjective determinants of ‘impact ’, ‘novelty’ or ‘interest’ ( 34 ). It works on a “lifetime publishing plan” model which charges scientists for publishing plans that give them lifetime rights to publish with PeerJ, rather than charging them per publication ( 34 ). PeerJ also encourages open peer review, and authors are given the option to post the full peer review history of their submission with their published article ( 34 ). PeerJ also offers a pre-print review service called PeerJ Pre-prints, in which paper drafts are reviewed before being sent to PeerJ to publish ( 34 ).
Rubriq is an independent peer review service designed by Shashi Mudunuri and Keith Collier to improve the peer review system ( 35 ). Rubriq is intended to decrease redundancy in the peer review process so that the time lost in redundant reviewing can be put back into research ( 35 ). According to Keith Collier, over 15 million hours are lost each year to redundant peer review, as papers get rejected from one journal and are subsequently submitted to a less prestigious journal where they are reviewed again ( 35 ). Authors often have to submit their manuscript to multiple journals, and are often rejected multiple times before they find the right match. This process could take months or even years ( 35 ). Rubriq makes peer review portable in order to help authors choose the journal that is best suited for their manuscript from the beginning, thus reducing the time before their paper is published ( 35 ). Rubriq operates under an author-pay model, in which the author pays a fee and their manuscript undergoes double-blind peer review by three expert academic reviewers using a standardized scorecard ( 35 ). The majority of the author’s fee goes towards a reviewer honorarium ( 35 ). The papers are also screened for plagiarism using iThenticate ( 35 ). Once the manuscript has been reviewed by the three experts, the most appropriate journal for submission is determined based on the topic and quality of the paper ( 35 ). The paper is returned to the author in 1-2 weeks with the Rubriq Report ( 35 ). The author can then submit their paper to the suggested journal with the Rubriq Report attached. The Rubriq Report will give the journal editors a much stronger incentive to consider the paper as it shows that three experts have recommended the paper to them ( 35 ). Rubriq also has its benefits for reviewers; the Rubriq scorecard gives structure to the peer review process, and thus makes it consistent and efficient, which decreases time and stress for the reviewer. Reviewers also receive feedback on their reviews and most significantly, they are compensated for their time ( 35 ). Journals also benefit, as they receive pre-screened papers, reducing the number of papers sent to their own reviewers, which often end up rejected ( 35 ). This can reduce reviewer fatigue, and allow only higher-quality articles to be sent to their peer reviewers ( 35 ).
According to Eva Amsen, peer review and scientific publishing are moving in a new direction, in which all papers will be posted online, and a post-publication peer review will take place that is independent of specific journal criteria and solely focused on improving paper quality ( 32 ). Journals will then choose papers that they find relevant based on the peer reviews and publish those papers as a collection ( 32 ). In this process, peer review and individual journals are uncoupled ( 32 ). In Keith Collier’s opinion, post-publication peer review is likely to become more prevalent as a complement to pre-publication peer review, but not as a replacement ( 35 ). Post-publication peer review will not serve to identify errors and fraud but will provide an additional measurement of impact ( 35 ). Collier also believes that as journals and publishers consolidate into larger systems, there will be stronger potential for “cascading” and shared peer review ( 35 ).
Peer review has become fundamental in assisting editors in selecting credible, high quality, novel and interesting research papers to publish in scientific journals and to ensure the correction of any errors or issues present in submitted papers. Though the peer review process still has some flaws and deficiencies, a more suitable screening method for scientific papers has not yet been proposed or developed. Researchers have begun and must continue to look for means of addressing the current issues with peer review to ensure that it is a full-proof system that ensures only quality research papers are released into the scientific community.
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John Cook 1,2,3 , Dana Nuccitelli 2,4 , Sarah A Green 5 , Mark Richardson 6 , Bärbel Winkler 2 , Rob Painting 2 , Robert Way 7 , Peter Jacobs 8 and Andrew Skuce 2,9
Published 15 May 2013 • © 2013 IOP Publishing Ltd Environmental Research Letters , Volume 8 , Number 2 Citation John Cook et al 2013 Environ. Res. Lett. 8 024024 DOI 10.1088/1748-9326/8/2/024024
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1 Global Change Institute, University of Queensland, Australia
2 Skeptical Science, Brisbane, Queensland, Australia
3 School of Psychology, University of Western Australia, Australia
4 Tetra Tech, Incorporated, McClellan, CA, USA
5 Department of Chemistry, Michigan Technological University, USA
6 Department of Meteorology, University of Reading, UK
7 Department of Geography, Memorial University of Newfoundland, Canada
8 Department of Environmental Science and Policy, George Mason University, USA
9 Salt Spring Consulting Ltd, Salt Spring Island, BC, Canada
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We analyze the evolution of the scientific consensus on anthropogenic global warming (AGW) in the peer-reviewed scientific literature, examining 11 944 climate abstracts from 1991–2011 matching the topics 'global climate change' or 'global warming'. We find that 66.4% of abstracts expressed no position on AGW, 32.6% endorsed AGW, 0.7% rejected AGW and 0.3% were uncertain about the cause of global warming. Among abstracts expressing a position on AGW, 97.1% endorsed the consensus position that humans are causing global warming. In a second phase of this study, we invited authors to rate their own papers. Compared to abstract ratings, a smaller percentage of self-rated papers expressed no position on AGW (35.5%). Among self-rated papers expressing a position on AGW, 97.2% endorsed the consensus. For both abstract ratings and authors' self-ratings, the percentage of endorsements among papers expressing a position on AGW marginally increased over time. Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research.
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An accurate perception of the degree of scientific consensus is an essential element to public support for climate policy (Ding et al 2011 ). Communicating the scientific consensus also increases people's acceptance that climate change (CC) is happening (Lewandowsky et al 2012 ). Despite numerous indicators of a consensus, there is wide public perception that climate scientists disagree over the fundamental cause of global warming (GW; Leiserowitz et al 2012 , Pew 2012 ). In the most comprehensive analysis performed to date, we have extended the analysis of peer-reviewed climate papers in Oreskes ( 2004 ). We examined a large sample of the scientific literature on global CC, published over a 21 year period, in order to determine the level of scientific consensus that human activity is very likely causing most of the current GW (anthropogenic global warming, or AGW).
Surveys of climate scientists have found strong agreement (97–98%) regarding AGW amongst publishing climate experts (Doran and Zimmerman 2009 , Anderegg et al 2010 ). Repeated surveys of scientists found that scientific agreement about AGW steadily increased from 1996 to 2009 (Bray 2010 ). This is reflected in the increasingly definitive statements issued by the Intergovernmental Panel on Climate Change on the attribution of recent GW (Houghton et al 1996 , 2001 , Solomon et al 2007 ).
The peer-reviewed scientific literature provides a ground-level assessment of the degree of consensus among publishing scientists. An analysis of abstracts published from 1993–2003 matching the search 'global climate change' found that none of 928 papers disagreed with the consensus position on AGW (Oreskes 2004 ). This is consistent with an analysis of citation networks that found a consensus on AGW forming in the early 1990s (Shwed and Bearman 2010 ).
Despite these independent indicators of a scientific consensus, the perception of the US public is that the scientific community still disagrees over the fundamental cause of GW. From 1997 to 2007, public opinion polls have indicated around 60% of the US public believes there is significant disagreement among scientists about whether GW was happening (Nisbet and Myers 2007 ). Similarly, 57% of the US public either disagreed or were unaware that scientists agree that the earth is very likely warming due to human activity (Pew 2012 ).
Through analysis of climate-related papers published from 1991 to 2011, this study provides the most comprehensive analysis of its kind to date in order to quantify and evaluate the level and evolution of consensus over the last two decades.
This letter was conceived as a 'citizen science' project by volunteers contributing to the Skeptical Science website ( www.skepticalscience.com ). In March 2012, we searched the ISI Web of Science for papers published from 1991–2011 using topic searches for 'global warming' or 'global climate change'. Article type was restricted to 'article', excluding books, discussions, proceedings papers and other document types. The search was updated in May 2012 with papers added to the Web of Science up to that date.
We classified each abstract according to the type of research (category) and degree of endorsement. Written criteria were provided to raters for category (table 1 ) and level of endorsement of AGW (table 2 ). Explicit endorsements were divided into non-quantified (e.g., humans are contributing to global warming without quantifying the contribution) and quantified (e.g., humans are contributing more than 50% of global warming, consistent with the 2007 IPCC statement that most of the global warming since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations).
Table 1. Definitions of each type of research category.
Category | Description | Example |
---|---|---|
(1) Impacts | Effects and impacts of climate change on the environment, ecosystems or humanity | '...global climate change together with increasing direct impacts of human activities, such as fisheries, are affecting the population dynamics of marine top predators' |
(2) Methods | Focus on measurements and modeling methods, or basic climate science not included in the other categories | 'This paper focuses on automating the task of estimating Polar ice thickness from airborne radar data...' |
(3) Mitigation | Research into lowering CO emissions or atmospheric CO levels | 'This paper presents a new approach for a nationally appropriate mitigation actions framework that can unlock the huge potential for greenhouse gas mitigation in dispersed energy end-use sectors in developing countries' |
(4) Not climate-related | Social science, education, research about people's views on climate | 'This paper discusses the use of multimedia techniques and augmented reality tools to bring across the risks of global climate change' |
(5) Opinion | Not peer-reviewed articles | 'While the world argues about reducing global warming, chemical engineers are getting on with the technology. Charles Butcher has been finding out how to remove carbon dioxide from flue gas' |
(6) Paleoclimate | Examining climate during pre-industrial times | 'Here, we present a pollen-based quantitative temperature reconstruction from the midlatitudes of Australia that spans the last 135 000 years...' |
Table 2. Definitions of each level of endorsement of AGW.
Level of endorsement | Description | Example |
---|---|---|
(1) Explicit endorsement with quantification | Explicitly states that humans are the primary cause of recent global warming | 'The global warming during the 20th century is caused mainly by increasing greenhouse gas concentration especially since the late 1980s' |
(2) Explicit endorsement without quantification | Explicitly states humans are causing global warming or refers to anthropogenic global warming/climate change as a known fact | 'Emissions of a broad range of greenhouse gases of varying lifetimes contribute to global climate change' |
(3) Implicit endorsement | Implies humans are causing global warming. E.g., research assumes greenhouse gas emissions cause warming without explicitly stating humans are the cause | '...carbon sequestration in soil is important for mitigating global climate change' |
(4a) No position | Does not address or mention the cause of global warming | |
(4b) Uncertain | Expresses position that human's role on recent global warming is uncertain/undefined | 'While the extent of human-induced global warming is inconclusive...' |
(5) Implicit rejection | Implies humans have had a minimal impact on global warming without saying so explicitly E.g., proposing a natural mechanism is the main cause of global warming | '...anywhere from a major portion to all of the warming of the 20th century could plausibly result from natural causes according to these results' |
(6) Explicit rejection without quantification | Explicitly minimizes or rejects that humans are causing global warming | '...the global temperature record provides little support for the catastrophic view of the greenhouse effect' |
(7) Explicit rejection with quantification | Explicitly states that humans are causing less than half of global warming | 'The human contribution to the CO content in the atmosphere and the increase in temperature is negligible in comparison with other sources of carbon dioxide emission' |
Abstracts were randomly distributed via a web-based system to raters with only the title and abstract visible. All other information such as author names and affiliations, journal and publishing date were hidden. Each abstract was categorized by two independent, anonymized raters. A team of 12 individuals completed 97.4% (23 061) of the ratings; an additional 12 contributed the remaining 2.6% (607). Initially, 27% of category ratings and 33% of endorsement ratings disagreed. Raters were then allowed to compare and justify or update their rating through the web system, while maintaining anonymity. Following this, 11% of category ratings and 16% of endorsement ratings disagreed; these were then resolved by a third party.
Upon completion of the final ratings, a random sample of 1000 'No Position' category abstracts were re-examined to differentiate those that did not express an opinion from those that take the position that the cause of GW is uncertain. An 'Uncertain' abstract explicitly states that the cause of global warming is not yet determined (e.g., '...the extent of human-induced global warming is inconclusive...') while a 'No Position' abstract makes no statement on AGW.
To complement the abstract analysis, email addresses for 8547 authors were collected, typically from the corresponding author and/or first author. For each year, email addresses were obtained for at least 60% of papers. Authors were emailed an invitation to participate in a survey in which they rated their own published papers (the entire content of the article, not just the abstract) with the same criteria as used by the independent rating team. Details of the survey text are provided in the supplementary information (available at stacks.iop.org/ERL/8/024024/mmedia ).
The ISI search generated 12 465 papers. Eliminating papers that were not peer-reviewed (186), not climate-related (288) or without an abstract (47) reduced the analysis to 11 944 papers written by 29 083 authors and published in 1980 journals. To simplify the analysis, ratings were consolidated into three groups: endorsements (including implicit and explicit; categories 1–3 in table 2 ), no position (category 4) and rejections (including implicit and explicit; categories 5–7).
We examined four metrics to quantify the level of endorsement:
Table 3. Abstract ratings for each level of endorsement, shown as percentage and total number of papers.
Position | % of all abstracts | % among abstracts with AGW position (%) | % of all authors | % among authors with AGW position (%) |
---|---|---|---|---|
Endorse AGW | 32.6% (3896) | 97.1 | 34.8% (10 188) | 98.4 |
No AGW position | 66.4% (7930) | — | 64.6% (18 930) | — |
Reject AGW | 0.7% (78) | 1.9 | 0.4% (124) | 1.2 |
Uncertain on AGW | 0.3% (40) | 1.0 | 0.2% (44) | 0.4 |
Among abstracts that expressed a position on AGW, 97.1% endorsed the scientific consensus. Among scientists who expressed a position on AGW in their abstract, 98.4% endorsed the consensus.
The time series of each level of endorsement of the consensus on AGW was analyzed in terms of the number of abstracts (figure 1 (a)) and the percentage of abstracts (figure 1 (b)). Over time, the no position percentage has increased (simple linear regression trend 0.87% ± 0.28% yr −1 , 95% CI, R 2 = 0.66, p < 0.001) and the percentage of papers taking a position on AGW has equally decreased.
Figure 1. (a) Total number of abstracts categorized into endorsement, rejection and no position. (b) Percentage of endorsement, rejection and no position/undecided abstracts. Uncertain comprise 0.5% of no position abstracts.
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The average numbers of authors per endorsement abstract (3.4) and per no position abstract (3.6) are both significantly larger than the average number of authors per rejection abstract (2.0). The scientists originated from 91 countries (identified by email address) with the highest representation from the USA ( N = 2548) followed by the United Kingdom ( N = 546), Germany ( N = 404) and Japan ( N = 379) (see supplementary table S1 for full list, available at stacks.iop.org/ERL/8/024024/mmedia ).
We emailed 8547 authors an invitation to rate their own papers and received 1200 responses (a 14% response rate). After excluding papers that were not peer-reviewed, not climate-related or had no abstract, 2142 papers received self-ratings from 1189 authors. The self-rated levels of endorsement are shown in table 4 . Among self-rated papers that stated a position on AGW, 97.2% endorsed the consensus. Among self-rated papers not expressing a position on AGW in the abstract, 53.8% were self-rated as endorsing the consensus. Among respondents who authored a paper expressing a view on AGW, 96.4% endorsed the consensus.
Table 4. Self-ratings for each level of endorsement, shown as percentage and total number of papers.
Position | % of all papers | % among papers with AGW position (%) | % of respondents | % among respondents with AGW position (%) |
---|---|---|---|---|
Endorse AGW | 62.7% (1342) | 97.2 | 62.7% (746) | 96.4 |
No AGW position | 35.5% (761) | — | 34.9% (415) | — |
Reject AGW | 1.8% (39) | 2.8 | 2.4% (28) | 3.6 |
a Self-rated papers that endorse AGW have an average endorsement rating less than 4 (1 =explicit endorsement with quantification, 7 = explicit rejection with quantification). b Undecided self-rated papers have an average rating equal to 4. c Rejection self-rated papers have an average rating greater than 4.
Figure 2 (a) shows the level of self-rated endorsement in terms of number of abstracts (the corollary to figure 1 (a)) and figure 2 (b) shows the percentage of abstracts (the corollary to figure 1 (b)). The percentage of self-rated rejection papers decreased (simple linear regression trend −0.25% ± 0.18% yr −1 , 95% CI, R 2 = 0.28, p = 0.01, figure 2 (b)). The time series of self-rated no position and consensus endorsement papers both show no clear trend over time.
Figure 2. (a) Total number of endorsement, rejection and no position papers as self-rated by authors. Year is the published year of each self-rated paper. (b) Percentage of self-rated endorsement, rejection and no position papers.
A direct comparison of abstract rating versus self-rating endorsement levels for the 2142 papers that received a self-rating is shown in table 5 . More than half of the abstracts that we rated as 'No Position' or 'Undecided' were rated 'Endorse AGW' by the paper's authors.
Table 5. Comparison of our abstract rating to self-rating for papers that received self-ratings.
Position | Abstract rating | Self-rating |
---|---|---|
Endorse AGW | 791 (36.9%) | 1342 (62.7%) |
No AGW position or undecided | 1339 (62.5%) | 761 (35.5%) |
Reject AGW | 12 (0.6%) | 39 (1.8%) |
Figure 3 compares the percentage of papers endorsing the scientific consensus among all papers that express a position endorsing or rejecting the consensus. The year-to-year variability is larger in the self-ratings than in the abstract ratings due to the smaller sample sizes in the early 1990s. The percentage of AGW endorsements for both self-rating and abstract-rated papers increase marginally over time (simple linear regression trends 0.10 ± 0.09% yr −1 , 95% CI, R 2 = 0.20, p = 0.04 for abstracts, 0.35 ± 0.26% yr −1 , 95% CI, R 2 = 0.26, p = 0.02 for self-ratings), with both series approaching approximately 98% endorsements in 2011.
Figure 3. Percentage of papers endorsing the consensus among only papers that express a position endorsing or rejecting the consensus.
Of note is the large proportion of abstracts that state no position on AGW. This result is expected in consensus situations where scientists ' ...generally focus their discussions on questions that are still disputed or unanswered rather than on matters about which everyone agrees ' (Oreskes 2007 , p 72). This explanation is also consistent with a description of consensus as a 'spiral trajectory' in which ' initially intense contestation generates rapid settlement and induces a spiral of new questions ' (Shwed and Bearman 2010 ); the fundamental science of AGW is no longer controversial among the publishing science community and the remaining debate in the field has moved to other topics. This is supported by the fact that more than half of the self-rated endorsement papers did not express a position on AGW in their abstracts.
The self-ratings by the papers' authors provide insight into the nature of the scientific consensus amongst publishing scientists. For both self-ratings and our abstract ratings, the percentage of endorsements among papers expressing a position on AGW marginally increased over time, consistent with Bray ( 2010 ) in finding a strengthening consensus.
The process of determining the level of consensus in the peer-reviewed literature contains several sources of uncertainty, including the representativeness of the sample, lack of clarity in the abstracts and subjectivity in rating the abstracts.
We address the issue of representativeness by selecting the largest sample to date for this type of literature analysis. Nevertheless, 11 944 papers is only a fraction of the climate literature. A Web of Science search for 'climate change' over the same period yields 43 548 papers, while a search for 'climate' yields 128 440 papers. The crowd-sourcing techniques employed in this analysis could be expanded to include more papers. This could facilitate an approach approximating the methods of Doran and Zimmerman ( 2009 ), which measured the level of scientific consensus for varying degrees of expertise in climate science. A similar approach could analyze the level of consensus among climate papers depending on their relevance to the attribution of GW.
Another potential area of uncertainty involved the text of the abstracts themselves. In some cases, ambiguous language made it difficult to ascertain the intended meaning of the authors. Naturally, a short abstract could not be expected to communicate all the details of the full paper. The implementation of the author self-rating process allowed us to look beyond the abstract. A comparison between self-ratings and abstract ratings revealed that categorization based on the abstract alone underestimates the percentage of papers taking a position on AGW.
Lastly, some subjectivity is inherent in the abstract rating process. While criteria for determining ratings were defined prior to the rating period, some clarifications and amendments were required as specific situations presented themselves. Two sources of rating bias can be cited: first, given that the raters themselves endorsed the scientific consensus on AGW, they may have been more likely to classify papers as sharing that endorsement. Second, scientific reticence (Hansen 2007 ) or 'erring on the side of least drama' (ESLD; Brysse et al 2012 ) may have exerted an opposite effect by biasing raters towards a 'no position' classification. These sources of bias were partially addressed by the use of multiple independent raters and by comparing abstract rating results to author self-ratings. A comparison of author ratings of the full papers and abstract ratings reveals a bias toward an under-counting of endorsement papers in the abstract ratings (mean difference 0.6 in units of endorsement level). This mitigated concerns about rater subjectivity, but suggests that scientific reticence and ESLD remain possible biases in the abstract ratings process. The potential impact of initial rating disagreements was also calculated and found to have minimal impact on the level of consensus (see supplemental information, section S1 available at stacks.iop.org/ERL/8/024024/mmedia ).
Our sample encompasses those surveyed by Oreskes ( 2004 ) and Schulte ( 2008 ) and we can therefore directly compare the results. Oreskes ( 2004 ) analyzed 928 papers from 1993 to 2003. Over the same period, we found 932 papers matching the search phrase 'global climate change' (papers continue to be added to the ISI database). From that subset we eliminated 38 papers that were not peer-reviewed, climate-related or had no abstract. Of the remaining 894, none rejected the consensus, consistent with Oreskes' result. Oreskes determined that 75% of papers endorsed the consensus, based on the assumption that mitigation and impact papers implicitly endorse the consensus. By comparison, we found that 28% of the 894 abstracts endorsed AGW while 72% expressed no position. Among the 71 papers that received self-ratings from authors, 69% endorse AGW, comparable to Oreskes' estimate of 75% endorsements.
An analysis of 539 'global climate change' abstracts from the Web of Science database over January 2004 to mid-February 2007 found 45% endorsement and 6% rejection (Schulte 2008 ). Our analysis over a similar period (including all of February 2007) produced 529 papers—the reason for this discrepancy is unclear as Schulte's exact methodology is not provided. Schulte estimated a higher percentage of endorsements and rejections, possibly because the strict methodology we adopted led to a greater number of 'No Position' abstracts. Schulte also found a significantly greater number of rejection papers, including 6 explicit rejections compared to our 0 explicit rejections. See the supplementary information (available at stacks.iop.org/ERL/8/024024/mmedia ) for a tabulated comparison of results. Among 58 self-rated papers, only one (1.7%) rejected AGW in this sample. Over the period of January 2004 to February 2007, among 'global climate change' papers that state a position on AGW, we found 97% endorsements.
The public perception of a scientific consensus on AGW is a necessary element in public support for climate policy (Ding et al 2011 ). However, there is a significant gap between public perception and reality, with 57% of the US public either disagreeing or unaware that scientists overwhelmingly agree that the earth is warming due to human activity (Pew 2012 ).
Contributing to this 'consensus gap' are campaigns designed to confuse the public about the level of agreement among climate scientists. In 1991, Western Fuels Association conducted a $510 000 campaign whose primary goal was to ' reposition global warming as theory (not fact) '. A key strategy involved constructing the impression of active scientific debate using dissenting scientists as spokesmen (Oreskes 2010 ). The situation is exacerbated by media treatment of the climate issue, where the normative practice of providing opposing sides with equal attention has allowed a vocal minority to have their views amplified (Boykoff and Boykoff 2004 ). While there are indications that the situation has improved in the UK and USA prestige press (Boykoff 2007 ), the UK tabloid press showed no indication of improvement from 2000 to 2006 (Boykoff and Mansfield 2008 ).
The narrative presented by some dissenters is that the scientific consensus is ' ...on the point of collapse ' (Oddie 2012 ) while ' ...the number of scientific "heretics" is growing with each passing year ' (Allègre et al 2012 ). A systematic, comprehensive review of the literature provides quantitative evidence countering this assertion. The number of papers rejecting AGW is a miniscule proportion of the published research, with the percentage slightly decreasing over time. Among papers expressing a position on AGW, an overwhelming percentage (97.2% based on self-ratings, 97.1% based on abstract ratings) endorses the scientific consensus on AGW.
Thanks to James Powell for his invaluable contribution to this analysis, Stephan Lewandowsky for his comments and to those who assisted with collecting email addresses and rating abstracts: Ari Jokimäki, Riccardo Reitano, Rob Honeycutt, Wendy Cook, Phil Scadden, Glenn Tamblyn, Anne-Marie Blackburn, John Hartz, Steve Brown, George Morrison, Alexander C Coulter, Martin B Stolpe (to name just those who are not listed as (co-)author to this paper).
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To date, no study has critically reviewed the current literature on the association between magnesium (Mg) and sleep health. Therefore, we carried out a systematic review to assess the association between Mg and sleep patterns in adults' population through observational and interventional studies. We searched for relevant studies through PubMed ( http://www.ncbi.nlm.nih.gov/pubmed ), Scopus ( http://www.scopus.com ), and ISI Web of Science ( http://www.webofscience.com ) from the earliest available date until November 2021. Eligibility criteria for study selection were guided by the following components identified using the PI(E)CO (Population, Intervention (Exposure), Comparison, Outcome) framework: P (adult population), I(E) (high dietary intake or supplementation of Mg), C (low dietary intake of Mg or placebo group), and O (sleep pattern including sleep duration, sleep-onset latency, night awakenings, sleep stages, and sleep phases). The present study involved 7,582 subjects from 9 published cross-sectional, cohort, and RCT systematically reviewed the possible links between Mg and sleep quality (daytime falling asleep, sleepiness, snoring, and sleep duration) in an adult population. Observational studies suggested an association between Mg statuses and sleep quality, while the RCTs reported contradictory findings. This systematic review revealed an association between magnesium status and sleep quality (daytime falling asleep, sleepiness, snoring, and sleep duration) according to the observational studies, while the randomized clinical trials showed an uncertain association between magnesium supplementation and sleep disorders. The association between dietary magnesium and sleep patterns needs well-designed randomized clinical trials with a larger sample size and longer follow-up time (more than 12 weeks) to further clarify the relationship.
Keywords: Magnesium; Nutrition; Sleep pattern; Sleep quality.
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3 Food Security Research Center, Isfahan University of Medical Sciences, Hezar Jarib St., 8174673461, Isfahan, Iran. [email protected]. PMID: 35184264. DOI: 10.1007/s12011-022-03162-1. Free article. Item in Clipboard. The Role of Magnesium in Sleep Health: a Systematic Review of Available Literature.
supervisors to author, or co-author a scientific paper to be submitted for publication. The NOAA Framework document (see section 1, above) requires papers submitted by NOAA authors to peer-reviewed literature to undergo an internal peer review process. The internal review is