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Research Methods & Reporting

Synthesis without meta-analysis (SWiM) in systematic reviews: reporting guideline

BMJ 2020; 368 doi: https://doi.org/10.1136/bmj.l6890 (Published 16 January 2020) Cite this as: BMJ 2020;368:l6890

Linked Opinion

Grasping the nettle of narrative synthesis

  1. Mhairi Campbell, research associate1,
  2. Joanne E McKenzie, associate professor2,
  3. Amanda Sowden, professor3,
  4. Srinivasa Vittal Katikireddi, clinical senior research fellow1,
  5. Sue E Brennan, research fellow2,
  6. Simon Ellis, associate director4,
  7. Jamie Hartmann-Boyce, senior researcher5,
  8. Rebecca Ryan, senior esearch fellow6,
  9. Sasha Shepperd, professor7,
  10. James Thomas, professor8,
  11. Vivian Welch, associate professor9,
  12. Hilary Thomson, senior research fellow1
  1. 1MRC/CSO Social and Public Health Sciences Unit, University of Glasgow, UK
  2. 2School of Public Health and Preventive Medicine, Monash University, Melbourne, Australia
  3. 3Centre for Reviews and Dissemination, University of York, York, UK
  4. 4Centre for Guidelines, National Institute for Health and Care Excellence, London, UK
  5. 5Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK
  6. 6School of Psychology and Public Health, La Trobe University, Melbourne, Australia
  7. 7Nuffield Department of Population Health, University of Oxford, Oxford, UK
  8. 8Evidence for Policy and Practice Information and Coordinating Centre, University College London, London, UK
  9. 9Bruyere Research Institute, Ottawa, Canada
  1. Correspondence to: M Campbell Mhairi.Campbell{at}glasgow.ac.uk
  • Accepted 8 October 2019

In systematic reviews that lack data amenable to meta-analysis, alternative synthesis methods are commonly used, but these methods are rarely reported. This lack of transparency in the methods can cast doubt on the validity of the review findings. The Synthesis Without Meta-analysis (SWiM) guideline has been developed to guide clear reporting in reviews of interventions in which alternative synthesis methods to meta-analysis of effect estimates are used. This article describes the development of the SWiM guideline for the synthesis of quantitative data of intervention effects and presents the nine SWiM reporting items with accompanying explanations and examples.

Summary points

  • Systematic reviews of health related interventions often use alternative methods of synthesis to meta-analysis of effect estimates, methods often described as “narrative synthesis”

  • Serious shortcomings in reviews that use “narrative synthesis” have been identified, including a lack of description of the methods used; unclear links between the included data, the synthesis, and the conclusions; and inadequate reporting of the limitations of the synthesis

  • The Synthesis Without Meta-analysis (SWiM) guideline is a nine item checklist to promote transparent reporting for reviews of interventions that use alternative synthesis methods

  • The SWiM items prompt users to report how studies are grouped, the standardised metric used for the synthesis, the synthesis method, how data are presented, a summary of the synthesis findings, and limitations of the synthesis

  • The SWiM guideline has been developed using a best practice approach, involving extensive consultation and formal consensus

Decision makers consider systematic reviews to be an essential source of evidence.1 Complete and transparent reporting of the methods and results of reviews allows users to assess the validity of review findings. The Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA; http://www.prisma-statement.org/) statement, consisting of a 27 item checklist, was developed to facilitate improved reporting of systematic reviews.2 Extensions are …

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