![]() ![]() However, underpowered studies made up the entirety of the evidence in most Cochrane reviews. Meta-analysis is a statistical method for pooling the results of several studies reporting the same outcome, in order to gain a better estimate of the effect size of an intervention. When at least two adequately powered studies are available in meta-analyses reported by Cochrane reviews, underpowered studies often contribute little information, and could be left out if a rapid review of the evidence is required. The standard error of the intervention effect increased by a median of 11% (inter-quartile range -1% to 35%) when underpowered studies were omitted and between-study heterogeneity tended to decrease. In the subset examined, odds ratios in underpowered studies were 15% lower (95% CI 11% to 18%, P<0.0001) than in adequately powered studies, in meta-analyses of controlled pharmacological trials and 12% lower (95% CI 7% to 17%, P<0.0001) in meta-analyses of controlled non-pharmacological trials. The median of summary relative risks was 0.75 across all meta-analyses (inter-quartile range 0.55 to 0.89). 34% of the meta-analyses themselves were adequately powered. PMA has been lauded as a ‘next generation’ method, 2 and Ioannidis has argued that all primary original research may be designed, executed, and interpreted as prospective meta. In 10,492 (70%) of 14,886 meta-analyses, all included studies were underpowered only 2,588 (17%) included at least two adequately powered studies. Prospective metaanalysis (PMA) is now gaining traction as a means of reducing research waste and producing meaningful and less biased evidence syntheses. In a subset of 1,107 meta-analyses including 5 or more studies with at least two adequately powered and at least one underpowered, results were compared with and without underpowered studies. We defined adequate power as ≥50% power to detect a 30% relative risk reduction. We examine the distribution of power available in studies within meta-analyses published in Cochrane reviews, and investigate the impact of underpowered studies on meta-analysis results.įor 14,886 meta-analyses of binary outcomes from 1,991 Cochrane reviews, we calculated power per study within each meta-analysis. The relative influence of adequately powered and underpowered studies in published meta-analyses has not previously been explored. Most meta-analyses include data from one or more small studies that, individually, do not have power to detect an intervention effect. A Re-Analysis of the Cochrane Library Data: The Dangers of Unobserved Heterogeneity in Meta-Analyses.
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