PRISMA 2020 explanation and elaboration. MetaArXiv preprint (September 2020) The following is the original version of the article submitted for publication in September 2020. The final published version is available at: Page MJ, Moher D, Bossuyt PM, Boutron I, Hoffmann TC, Mulrow CD, Shamseer L, Tetzlaff JM, Akl EA, Brennan SE, Chou R, Glanville J, Grimshaw JM, Hróbjartsson A, Lalu MM, Li T, Loder EW, Mayo- Wilson E, McDonald S, McGuinness LA, Stewart LA, Thomas J, Tricco AC, Welch VA, Whiting P, McKenzie JE. PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews. BMJ 2021;372:n160. DOI: 10.1136/bmj.n.160. PRISMA 2020 explanation and elaboration: updated guidance and exemplars for reporting systematic reviews Matthew J Page, senior research fellow1,*, David Moher, director and professor2,†, Patrick M Bossuyt, professor3, Isabelle Boutron, professor4, Tammy C Hoffmann, professor5, Cynthia D Mulrow, professor6, Larissa Shamseer, doctoral student7, Jennifer M Tetzlaff, research product specialist8, Elie A Akl, professor9, Sue E Brennan, senior research fellow1, Roger Chou, professor10, Julie Glanville, associate director11, Jeremy M Grimshaw, professor12, Asbjørn Hróbjartsson, professor13, Manoj M Lalu, associate scientist and assistant professor14, Tianjing Li, associate professor15, Elizabeth W Loder, professor16, Evan Mayo-Wilson, associate professor17, Steve McDonald, senior research fellow1, Luke A McGuinness, research associate18, Lesley A Stewart, professor and director19, James Thomas, professor20, Andrea C Tricco, scientist and associate professor21, Vivian A Welch, associate professor22, Penny Whiting, associate professor18, Joanne E McKenzie, associate professor1,† 1. School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia 2. Centre for Journalology, Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada 3. Department of Clinical Epidemiology, Biostatistics and Bioinformatics, Amsterdam University Medical Centres, University of Amsterdam, Amsterdam, Netherlands 4. Université de Paris, Centre of Epidemiology and Statistics (CRESS), Inserm, F 75004 Paris, France 5. Institute for Evidence-Based Healthcare, Faculty of Health Sciences and Medicine, Bond University, Gold Coast, Australia 6. University of Texas Health Science Center at San Antonio, San Antonio, Texas, United States; Annals of Internal Medicine PRISMA 2020 explanation and elaboration. MetaArXiv preprint (September 2020) 7. School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada 8. Evidence Partners, Ottawa, Canada 9. Clinical Research Institute, American University of Beirut, Beirut, Lebanon; Department of Health Research Methods, Evidence, and Impact, McMaster University, Hamilton, Ontario, Canada 10. Department of Medical Informatics and Clinical Epidemiology, Oregon Health & Science University, Portland, Oregon, United States 11. York Health Economics Consortium (YHEC Ltd), University of York, York, UK 12. Clinical Epidemiology Program, Ottawa Hospital Research Institute, Ottawa, Canada; School of Epidemiology and Public Health, University of Ottawa, Ottawa, Canada; Department of Medicine, University of Ottawa, Ottawa, Canada 13. Centre for Evidence-Based Medicine Odense, Odense University Hospital, Odense, Denmark; Department of Clinical Research, University of Southern Denmark, Odense, Denmark; Open Patient data Explorative Network, Odense University Hospital, Odense, Denmark 14. Department of Anesthesiology and Pain Medicine, The Ottawa Hospital, Ottawa, Canada; Clinical Epidemiology Program, Blueprint Translational Research Group, Ottawa Hospital Research Institute, Ottawa, Canada; Regenerative Medicine Program, Ottawa Hospital Research Institute, Ottawa, Canada 15. Department of Ophthalmology, School of Medicine, University of Colorado Denver, Denver, Colorado, United States; Department of Epidemiology, Johns Hopkins Bloomberg School of Public Health, Baltimore, Maryland, United States 16. Division of Headache, Department of Neurology, Brigham and Women's Hospital, Harvard Medical School, Boston, Massachusetts, United States; Head of Research, The BMJ, London, UK 17. Department of Epidemiology and Biostatistics, Indiana University School of Public Health- Bloomington, Bloomington, Indiana, United States 18. Population Health Sciences, Bristol Medical School, University of Bristol, Bristol, UK 19. Centre for Reviews and Dissemination, University of York, York, UK 20. EPPI-Centre, UCL Social Research Institute, University College London, London, UK 21. Li Ka Shing Knowledge Institute of St. Michael's Hospital, Unity Health Toronto, Toronto, Canada; Epidemiology Division of the Dalla Lana School of Public Health and the Institute of Health Management, Policy, and Evaluation, University of Toronto, Toronto, Canada; Queen's Collaboration for Health Care Quality Joanna Briggs Institute Centre of Excellence, Queen's University, Kingston, Canada PRISMA 2020 explanation and elaboration. MetaArXiv preprint (September 2020) 22. Methods Centre, Bruyère Research Institute, Ottawa, Ontario, Canada; School of Epidemiology and Public Health, Faculty of Medicine, University of Ottawa, Ottawa, Canada *Correspondence to: Dr. Matthew Page, School of Public Health and Preventive Medicine, Monash University, 553 St Kilda Road, Melbourne, Victoria, 3004, Australia. Telephone: +61 9903 0248. Email address: [email protected] †DM and JEM are joint senior authors. Dedication: We dedicate this paper to the late Douglas G Altman and Alessandro Liberati, whose contributions were fundamental to the development and implementation of the original PRISMA statement. PRISMA 2020 explanation and elaboration. MetaArXiv preprint (September 2020) ABSTRACT The methods and results of systematic reviews should be reported in sufficient detail to allow users to assess the trustworthiness and applicability of the review findings. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement was developed to facilitate transparent and complete reporting of systematic reviews and has been updated (to PRISMA 2020) to reflect recent advances in systematic review methodology and terminology. Here, we present the explanation and elaboration paper for PRISMA 2020, where we explain why reporting of each item is recommended, present bullet points that detail the reporting recommendations, and present exemplars from published reviews. We hope that changes to the content and structure of PRISMA 2020 will facilitate uptake of the guideline and lead to more transparent, complete and accurate reporting of systematic reviews. PRISMA 2020 explanation and elaboration. MetaArXiv preprint (September 2020) INTRODUCTION Systematic reviews are essential for health care providers, policy makers and other decision makers, who without them, would be confronted by an overwhelming volume of research on which to base their decisions. To allow decision makers to assess the trustworthiness and applicability of review findings, reports of systematic reviews should be transparent and complete. Furthermore, such reporting should allow others to replicate or update reviews. The Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement published in 2009 (hereafter referred to as PRISMA 2009) (1, 2) was designed to help authors prepare transparent accounts of their reviews, and its recommendations have been widely endorsed and adopted (3). We have updated the PRISMA 2009 statement (to PRISMA 2020) to ensure currency and relevance and to reflect advances in systematic review methodology and terminology. Scope of this guideline The PRISMA 2020 statement has been designed primarily for systematic reviews of studies that evaluate the effects of health interventions, irrespective of the design of the included studies. However, the checklist items are applicable to reports of systematic reviews evaluating other non- health-related interventions (e.g. social or educational interventions), and many items are applicable to systematic reviews with objectives other than evaluating interventions (e.g. evaluating aetiology, prevalence or prognosis). PRISMA 2020 is intended for use in systematic reviews that include synthesis (e.g. pairwise meta-analysis, or other statistical synthesis methods), or do not include synthesis (e.g. because only one eligible study is identified). The PRISMA 2020 items are relevant for mixed-methods systematic reviews (which include quantitative and qualitative studies), but reporting guidelines addressing the presentation and synthesis of qualitative data should also be consulted (4, 5). PRISMA 2020 can be used for original systematic reviews, updated systematic reviews, or continually updated (“living”) systematic reviews. Extensions to the PRISMA 2009 statement have been developed to guide reporting of network meta-analyses (6), meta-analyses of individual participant data (7), systematic reviews of harms (8), systematic reviews of diagnostic test accuracy studies (9) and scoping reviews (10); for these types of reviews we recommend authors report their review in accordance with the recommendations in PRISMA 2020 along with the guidance specific to the extension. PRISMA 2020 explanation and elaboration PRISMA 2020 is published as a suite of three papers: a statement paper, consisting of the 27-item