To the Editor: The selective reporting of outcomes in randomized controlled trials (RCTs), or outcome reporting bias, has been identified,1 but its prevalence and potential effect in meta-analyses is unknown. We investigated (1) to what extent Cochrane meta-analyses include only a proportion of identified RCTs when estimating treatment effects on patient-important outcomes and (2) whether the proportion of RCTs included in a meta-analysis is associated with its pooled effect size.
Furukawa TA, Watanabe N, Omori IM, Montori VM, Guyatt GH. Association Between Unreported Outcomes and Effect Size Estimates in Cochrane Meta-analyses. JAMA. 2007;297(5):465–470. doi:10.1001/jama.297.5.468-b
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