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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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