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Why reports of clinical trials should include updated meta-analyses
  1. Carl Heneghan,
  2. Jeffrey K Aronson
  1. Centre for Evidence-Based Medicine, Nuffield Department of Primary Care Health Sciences, University of Oxford, Oxford, UK
  1. Correspondence to Professor Carl Heneghan, Primary Care Health Sciences, University of Oxford, Oxford OX1 2JD, UK; carl.heneghan{at}

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In the BMJ-EBM Verdict series, Plüddemann and Onakpoya analysed the effects of endometrial scratching before in vitro fertilisation.1 Their verdict was that endometrial scratching does not result in higher live birth rates in women having a first embryo transfer, nor in those with previously failed transfers.

They reached their verdict by adding the results of a recent randomised controlled trial (RCT)2 to those of two previous systematic reviews.3 4 They meta-analysed the primary outcome and were therefore more confident in their conclusions than if they had analysed the results of the RCT alone. Onakpoya and Aronson did likewise when they updated their previous meta-analysis in the light of a new large trial and concluded that lorcaserin, marketed for the treatment of obesity, conferred minimal benefits.5

In neither case was a new systematic review performed, with all that entails. Instead the latest results on primary outcomes were added to existing meta-analyses, providing up-to-date information and paving the way for new systematic reviews, if necessary.

The value of systematic reviews

Systematic reviews are vital for informing research plans6 and for ensuring that treatment decisions are informed by evidence on treatment effects and costs, as in guideline development.7 In summarising the evidence from a large number of studies, systematic reviews and meta-analyses increase precision around effect estimates, producing more robust conclusions.

Even so, systematic reviews with meta-analyses often have insufficient power to detect, confirm, or refute the hoped-for effects of potentially useful interventions, …

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  • Contributors CH conceived the idea for the editorial and wrote the first draft; JKA added further discussion, and the two authors contributed equally to the final manuscript.

  • Funding The authors have not declared a specific grant for this research from any funding agency in the public, commercial or not-for-profit sectors.

  • Competing interests CH holds grant funding from the NIHR School of Primary Care Research Evidence Synthesis Working Group (project 390) and the NIHR Oxford BRC. He is editor in chief of BMJ Evidence-Based Medicine and an NIHR senior investigator. He is director of the Centre for Evidence-Based Medicine (CEBM), which jointly runs the EvidenceLive Conference with the BMJ and the Overdiagnosis Conference with some international partners, which are based on a non-profit model. JKA has written and edited articles and textbooks on adverse drug reactions, including Meyler’s Side Effects of Drugs (16th edition, 2016), its companion volumes the Side Effects of Drugs Annuals, and Stephens’ Detection and Evaluation of Adverse Drug Reactions (6th edition, 2011). He is an associate editor of BMJ Evidence-Based Medicine and a member of the CEBM (see above).

  • Patient consent for publication Not required.

  • Provenance and peer review Not commissioned; internally peer reviewed.

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