Review articles were and remain resources of major value across science. However, the landscape of review articles underwent major changes over the last 50 years. Whereas review articles in Medicine and Public Health in the pre-evidence-based era were almost exclusively unsystematic ¹1. Mulrow CD. The medical review article: state of the science. Ann Intern Med 1987; 106:485-8., the 1990s and the new millennium witnessed the rise of research synthesis as a scientific discipline in its own right ²2. Grant MJ, Booth A. A typology of reviews: an analysis of 14 review types and associated methodologies. Health Info Libr J 2009; 26:91-108.^,33. Chalmers I, Hedges LV, Cooper H. A brief history of research synthesis. Eval Health Prof 2002; 25:12-37.. For example, in 1999, about 300 systematic review references were indexed in PubMed, whereas 20 years later, in 2019, more than 27 thousand records of systematic reviews were added to that database. Not only did the number of reviews grow exponentially, the complexity and diversity of the review methods also underwent dramatic progress, to such an extent that it is often impossible for a single researcher to keep pace and master all the burgeoning advances in this field ⁴4. Nakagawa S, Samarasinghe G, Haddaway NR, Westgate MJ, O'Dea RE, Noble DWA, et al. Research weaving: visualizing the future of research synthesis. EcoEvoRxiv 2018; 10 nov. https://ecoevorxiv.org/ga2qz/ (acessado em 07/Mar/2021).
https://ecoevorxiv.org/ga2qz/... ^,55. Cacchione PZ. The evolving methodology of scoping reviews. Clin Nurs Res 2016; 25:115-9.^,66. Munn Z, Stern C, Aromataris E, Lockwood C, Jordan Z. What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences. BMC Med Res Methodol 2018; 18:5.^,77. Gough D, Thomas J, Oliver S. Clarifying differences between review designs and methods. Syst Rev 2012; 1:28..

But why are good literature reviews so important? The 1904 Nobel Prize laureate in Physics, John W. Strutt (Lord Rayleigh), in his presidential address to the British Association for the Advancement of Science in 1884, argued that the scientific endeavor is a process consisting of both the production of new knowledge and its integration with the old ⁸8. Lord Rayleigh. Report of the fifty-fourth meeting of the British Association for the Advancement of Science [microform]: held at Montreal in August and September 1884. https://archive.org/details/cihm_05877/page/n7/mode/2up?q=Rayleigh (acessado em 07/Mar/2021).
https://archive.org/details/cihm_05877/p... . He argued that if science consisted only in the accumulation of facts, it would be crushed by its own weight. In that regard, literature reviews play a major role in the judicious integration of new and old knowledge. Reviews are also valuable for providing historical context, pointing out gaps in the existing knowledge, and future directions ⁹9. Tay A. How to write a superb literature review. Nature 2020; [Online ahead of print].. Increasingly, a major driver of the rise of the research synthesis field involves the fact that high-quality reviews have been consumed and demanded not only by researchers and practitioners but also by policy makers and the public more generally ³3. Chalmers I, Hedges LV, Cooper H. A brief history of research synthesis. Eval Health Prof 2002; 25:12-37.. Indeed, both Cochrane (The Cochrane Collaboration. http://www.cochrane.org, accessed on 07/Mar/2021) and Campbell (The Campbell Collaboration. https://www.campbellcollaboration.org/, accessed on 07/Mar/2021) Collaborations offer plain-language summaries of their research syntheses on health and social science issues for laypeople.

Given the growing complexity of review methods, what advice can be given to novice researchers considering writing a review article? Our first advice concerns being clear about the aims of the review. Researchers should ask themselves why the review is needed and to which public it is intended. A clear understanding of the aims of the review will often signal the most appropriate methods to fulfill those aims. For instance, if researchers have a focused question regarding the efficacy/effectiveness of a certain practice or treatment on a given set of outcomes and aim for their synthesis to influence guidelines or policy, then a systematic review would be the method of choice. Importantly, there are at least 10 types of systematic reviews, ranging from economic evaluations to qualitative meta-synthesis ⁶6. Munn Z, Stern C, Aromataris E, Lockwood C, Jordan Z. What kind of systematic review should I conduct? A proposed typology and guidance for systematic reviewers in the medical and health sciences. BMC Med Res Methodol 2018; 18:5.. If they aim to understand the extent and nature of the literature on a given subject to determine the value and scope of future systematic reviews or gaps in the literature, then a scoping review would probably be the best approach to suit their needs ¹⁰10. Peters MDJ, Godfrey CM, Khalil H, McInerney P, Parker D, Soares CB. Guidance for conducting systematic scoping reviews. Int J Evid Based Healthc 2015; 13:141-6.. On the other hand, if researchers aim to provide a broad perspective on a certain subject, ranging from its history to recent advances, current standards, controversies, and future directions, then a narrative review would probably be the way to go ¹¹11. Gregory AT, Denniss AR. An introduction to writing narrative and systematic reviews - tasks, tips and traps for aspiring authors. Heart Lung Circ 2018; 27:893-8..

Our second piece of advice involves becoming very intimate with the fundamental principles and methods of the review approach that was chosen and building a review team whose collective expertise and commitment should be sufficient to address the main challenges of the review. For example, becoming familiar with the methods of systematic reviews of interventions demands a good understanding of the contents of the Cochrane ¹²12. Higgins JPT, Thomas J, Chandler J, Cumpston M, Li T, Page MJ, et al. Cochrane handbook for systematic reviews of interventions. 2nd Ed. Hoboken: Wiley-Blackwell; 2020. [Cochrane Book Series]. and GRADE ¹³13. Schünemann H, Brozek J, Guyatt G, Oxman A. GRADE handbook. https://gdt.gradepro.org/app/handbook/handbook.html (acessado em 07/Mar/2021).
https://gdt.gradepro.org/app/handbook/ha... Handbooks, the PRISMA statements (http://prisma-statement.org/, accessed on 07/Mar/2021), and the AMSTAR 2 tool ¹⁴14. Shea BJ, Reeves BC, Wells G, Thuku M, Hamel C, Moran J, et al. AMSTAR 2: a critical appraisal tool for systematic reviews that include randomised or non-randomised studies of healthcare interventions, or both. BMJ 2017; 358:j4008.. For scoping reviews, authors should be familiar with Arksey & O’Malley’s ¹⁵15. Arksey H, O'Malley L. Scoping studies: towards a methodological framework. Int J Soc Res Methodol 2005; 8:19-32. seminal work and recent developments ¹⁰10. Peters MDJ, Godfrey CM, Khalil H, McInerney P, Parker D, Soares CB. Guidance for conducting systematic scoping reviews. Int J Evid Based Healthc 2015; 13:141-6.^,1616. Tricco AC, Lillie E, Zarin W, O'Brien KK, Colquhoun H, Levac D, et al. PRISMA Extension for Scoping Reviews (PRISMA-ScR): checklist and Explanation. Ann Intern Med 2018; 169:467.^,1717. Levac D, Colquhoun H, O'Brien KK. Scoping studies: advancing the methodology. Implement Sci 2010; 5:69.. Although recently a scale was developed for the assessment of the quality of narrative reviews ¹⁸18. Baethge C, Goldbeck-Wood S, Mertens S. SANRA - a scale for the quality assessment of narrative review articles. Res Integr Peer Rev 2019 26; 4:5. that instrument seems far from ideal. Hence, for authors interested in narrative reviews, we recommend a close examination of the structure of narrative reviews published in the State of the Art series ¹⁹19. The BMJ. State of the Art. Latest from the BMJ. https://www.bmj.com/specialties/state-art (acessado em 07/Mar/2021).
https://www.bmj.com/specialties/state-ar... of the British Medical Journal, which provide broad overviews on the main subject while drawing as much as possible on the results of previous systematic reviews. Ideally, the review team should include at least one expert on the subject of the review and another on its specific methods.

Our last piece of advice regards what not to do in a review article. First, avoid at all costs tedious data presentation patterns where one engages in an extensive list of statements that author A found X, author B found Y, while author C found Z. Such approaches to the presentation of data do not lead to any palpable synthesis and easily become a source of dismay to readers. Second, avoid simplistic conclusions that do not take into account the complexity of the subject at hand, such as jumping to causal conclusions without considering the (un)certainty or quality of the evidence. Third, in systematic reviews, where the assessment of risk of bias is mandatory, avoid the use of instruments such as the Newcastle-Ottawa and Downs & Black Scales, that yield numeric scores as their final parameter for the evaluation of the risk of bias in included studies. Although commonly used, such tools will often fail to identify studies at high risk of bias when a single or few critical domains are severely compromised within studies included in the review ²⁰20. Vidal EIO. O que esperamos das revisões sistemáticas no futuro. Cad Saúde Pública 2016; 32:eED010916.^,2121. O'Connor SR, Tully MA, Ryan B, Bradley JM, Baxter GD, McDonough SM. Failure of a numerical quality assessment scale to identify potential risk of bias in a systematic review: a comparison study. BMC Res Notes 2015; 8:224.. Several instruments are currently available that avoid the illusion of objectivity posed by numeric scores to assess risk of bias. Those instruments require authors to think carefully about important issues such as the major sources of confounding within a certain causal framework of interest for their reviews (Risk of bias tools. https://sites.google.com/site/riskofbiastool/, accessed on 08/Mar/2021) ²²22. Joanna Briggs Institute. Critical appraisal tools. https://jbi.global/critical-appraisal-tools (acessado em 08/Mar/2021).
https://jbi.global/critical-appraisal-to... . Fourth, avoid the overuse of abbreviations and jargon that are habitual only for those within that specific field because reviews should be useful for a broad audience, including those who are approaching their subject for the first time ⁹9. Tay A. How to write a superb literature review. Nature 2020; [Online ahead of print].. Finally, do not attempt to disguise the introductory chapters of a thesis or dissertation as a review article. Although those introductory chapters are supposed to present a review of the literature, they have different aims, audience, and rigor than what is expected from a good review article.

In conclusion, good review articles dwell at the heart of the scientific endeavor. The craft of writing them involves a balancing act between the scientific rigor needed to select and critically appraise original studies, and the art of telling a story by providing context, exploring the known and the unknown, and pointing the way forward.

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