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Effect sizes in child health and association with unreported outcomes

Date and Location




Friday 20 September 2013 - 13:30 - 15:00


Presenting author and contact person

Presenting author

Lisa Hartling

Contact person

Lisa Hartling
Abstract text
Background: Research has shown that half of randomized controlled trials (RCTs) included in Cochrane systematic reviews do not contribute to the meta-analysis of patient-important outcomes. Further, previous research showed an inverse relationship with effect size and the proportion of RCTs contributing to the meta-analysis. One potential explanation for this finding is selective outcome reporting. Objectives: To describe effect sizes in pediatric RCTs and the association between the proportion of relevant RCTs contributing to a meta-analysis and the magnitude of effect. Methods: Using the Cochrane Database of Systematic Reviews we identified systematic reviews relevant to child health. We identified the primary outcome for each systematic review and extracted data when a meta-analysis had been conducted (n=432). We calculated an overall effect size for meta-analyses based on the proportion of relevant RCTs included using categories from previous research: <20, 20 to <40, 40 to <60, 60 to <80, ≥80%. Results: The median effect size across all meta-analyses was 0.35 (IQR 0.15,0.59) which is considered small to moderate. The mean proportion of relevant studies contributing to a meta-analysis was 0.49 (95%CI 0.47,0.52). There was no association between effect sizes and the proportion of RCTs contributing to a meta-analysis. However, effect sizes were associated with the size of the meta-analysis with smaller effect sizes seen with larger meta-analyses (i.e., smaller confidence intervals). Conclusions: We found an association between effect sizes and the size of meta-analysis. This effect is similar to that seen for publication bias at the individual study level. Caution should be taken when interpreting meta-analyses based on small numbers of studies and patients, which is consistent with the GRADE recommendations for considering imprecision. Effect sizes were small to moderate overall. These data may provide a guide for sample size calculations in future pediatric trials.