How Many Articles to Use in Literature Review

PLoS Comput Biol. 2013 Jul; 9(vii): e1003149.

Ten Simple Rules for Writing a Literature Review

Marco Pautasso

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

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

Philip East. Bourne, Editor

Literature reviews are in slap-up demand in nearly scientific fields. Their need stems from the e'er-increasing output of scientific publications [1]. For example, compared to 1991, in 2008 3, eight, and twoscore times more papers were indexed in Web of Science on malaria, obesity, and biodiversity, respectively [two]. Given such mountains of papers, scientists cannot be expected to examine in detail every unmarried new paper relevant to their interests [3]. Thus, information technology is both advantageous and necessary to rely on regular summaries of the recent literature. Although recognition for scientists mainly comes from primary research, timely literature reviews tin lead to new synthetic insights and are often widely read [iv]. For such summaries to be useful, however, they need to be compiled in a professional manner [five].

When starting from scratch, reviewing the literature tin require a titanic amount of work. That is why researchers who take spent their career working on a sure inquiry issue are in a perfect position to review that literature. Some graduate schools are now offer courses in reviewing the literature, given that most research students commencement their project by producing an overview of what has already been washed on their inquiry event [six]. Yet, it is likely that most scientists have not idea in item near how to approach and carry out a literature review.

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

Rule 1: Define a Topic and Audience

How to choose which topic to review? In that location are so many issues in contemporary science that you could spend a lifetime of attending conferences and reading the literature merely pondering what to review. On the 1 hand, if you take several years to choose, several other people may have had the same thought in the meantime. On the other hand, just a well-considered topic is likely to lead to a brilliant literature review [eight]. The topic must at to the lowest degree be:

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

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

Dominion 2: Search and Re-search the Literature

Subsequently having called your topic and audience, outset past checking the literature and downloading relevant papers. Five pieces of communication here:

keep track of the search items you use (and then that your search can exist replicated [ten]),
keep a list of papers whose pdfs you lot cannot access immediately (so equally to retrieve them later with alternative strategies),
utilise a paper direction system (e.g., Mendeley, Papers, Qiqqa, Sente),
ascertain early on in the process some criteria for exclusion of irrelevant papers (these criteria tin and then exist described in the review to help define its scope), and
practise non just look for inquiry papers in the expanse yous wish to review, but as well seek previous reviews.

The chances are loftier that someone will already have published a literature review (Effigy 1), if not exactly on the issue y'all are planning to tackle, at least on a related topic. If there are already a few or several reviews of the literature on your event, my advice is not to surrender, but to carry on with your own literature review,

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A conceptual diagram of the need for different types of literature reviews depending on the amount of published inquiry papers and literature reviews.

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

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

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

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

Rule 3: Accept Notes While Reading

If you lot read the papers first, and only later beginning writing the review, yous will need a very good retentivity to retrieve who wrote what, and what your impressions and associations were while reading each single newspaper. My communication is, while reading, to get-go writing downward interesting pieces of data, insights about how to organize the review, and thoughts on what to write. This mode, by the time y'all have read the literature you selected, you lot volition already accept a crude typhoon of the review.

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

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

After having taken notes while reading the literature, yous will have a crude idea of the amount of cloth available for the review. This is probably a skilful time to decide whether to go for a mini- or a full review. Some journals are now favouring the publication of rather brusque reviews focusing on the final few years, with a limit on the number of words and citations. A mini-review is not necessarily a small-scale review: it may well attract more attending from busy readers, although information technology volition inevitably simplify some problems and leave out some relevant material due to space limitations. A total review volition accept the advantage of more than liberty to comprehend in detail the complexities of a particular scientific development, but may and then be left in the pile of the very important papers "to be read" by readers with lilliputian time to spare for major monographs.

In that location is probably a continuum between mini- and full reviews. The same point applies to the dichotomy of descriptive vs. integrative reviews. While descriptive reviews focus on the methodology, findings, and estimation of each reviewed study, integrative reviews try to find common ideas and concepts from the reviewed material [12]. A similar distinction exists between narrative and systematic reviews: while narrative reviews are qualitative, systematic reviews try to test a hypothesis based on the published evidence, which is gathered using a predefined protocol to reduce bias [xiii], [14]. When systematic reviews analyse quantitative results in a quantitative way, they get meta-analyses. The choice between different review types will take to exist fabricated on a case-by-case basis, depending not merely on the nature of the material found and the preferences of the target periodical(s), but also on the time bachelor to write the review and the number of coauthors [fifteen].

Rule v: Go on the Review Focused, only Make It of Broad Involvement

Whether your programme is to write a mini- or a full review, it is good advice to keep information technology focused xvi,17. Including fabric just for the sake of it can hands lead to reviews that are trying to exercise too many things at once. The demand to go along a review focused can be problematic for interdisciplinary reviews, where the aim is to bridge the gap betwixt fields [18]. If you are writing a review on, for example, how epidemiological approaches are used in modelling the spread of ideas, you may exist inclined to include material from both parent fields, epidemiology and the report of cultural diffusion. This may be necessary to some extent, simply in this case a focused review would just deal in detail with those studies at the interface betwixt epidemiology and the spread of ideas.

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

Rule 6: Be Disquisitional and Consistent

Reviewing the literature is non stamp collecting. A practiced review does not just summarize the literature, but discusses information technology critically, identifies methodological problems, and points out enquiry gaps [nineteen]. After having read a review of the literature, a reader should have a rough thought of:

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

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

Rule 7: Find a Logical Structure

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

How can you organize the flow of the main body of the review and then that the reader volition be drawn into and guided through it? Information technology is more often than not helpful to draw a conceptual scheme of the review, eastward.g., with mind-mapping techniques. Such diagrams can help recognize a logical manner to order and link the various sections of a review [21]. This is the case not just at the writing stage, but besides for readers if the diagram is included in the review as a figure. A careful selection of diagrams and figures relevant to the reviewed topic can exist very helpful to structure the text as well [22].

Rule viii: Make Use of Feedback

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

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

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

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

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

Dominion 10: Be Up-to-Date, but Do Non Forget Older Studies

Given the progressive acceleration in the publication of scientific papers, today's reviews of the literature need sensation non only of the overall management and achievements of a field of inquiry, but also of the latest studies, and so as not to become out-of-appointment before they accept been published. Ideally, a literature review should non identify as a major research gap an upshot that has but been addressed in a serial of papers in press (the same applies, of grade, to older, overlooked studies ("sleeping beauties" [26])). This implies that literature reviewers would exercise well to go on an eye on electronic lists of papers in press, given that it tin take months before these appear in scientific databases. Some reviews declare that they have scanned the literature up to a certain signal in fourth dimension, but given that peer review can exist a rather lengthy process, a full search for newly appeared literature at the revision stage may be worthwhile. Assessing the contribution of papers that have just appeared is specially challenging, considering there is little perspective with which to judge their significance and impact on further research and society.

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

Acknowledgments

Many cheers to M. Barbosa, K. Dehnen-Schmutz, T. Döring, D. Fontaneto, 1000. Garbelotto, O. Holdenrieder, One thousand. Jeger, D. Lonsdale, A. MacLeod, P. Mills, M. Moslonka-Lefebvre, G. Stancanelli, P. Weisberg, and X. Xu for insights and discussions, and to P. Bourne, T. Matoni, and D. Smith for helpful comments on a previous typhoon.

Funding Statement

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

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