Influence of trial sample size on treatment effect estimates: meta-epidemiological study

Objective To assess the influence of trial sample size on treatment effect estimates within meta-analyses. Design Meta-epidemiological study. Data sources 93 meta-analyses (735 randomised controlled trials) assessing therapeutic interventions with binary outcomes, published in the 10 leading journals of each medical subject category of the Journal Citation Reports or in the Cochrane Database of Systematic Reviews. Data extraction Sample size, outcome data, and risk of bias extracted from each trial. Data synthesis Trials within each meta-analysis were sorted by their sample size: using quarters within each meta-analysis (from quarter 1 with 25% of the smallest trials, to quarter 4 with 25% of the largest trials), and using size groups across meta-analyses (ranging from