In the meta-analysis of a Cochrane review, the funnel plot shows clear asymmetry, with small trials clustering to one side of the pooled estimate and larger trials near its apex. The most appropriate interpretation of this finding is:

• A High heterogeneity requiring a fixed effects model
• B Probable publication bias or small-study effects ✓
• C Reverse causation in the included trials
• D Loss of allocation concealment in large trials

Explanation

Under no bias, trial estimates scatter symmetrically around the pooled effect, with spread widening as precision falls. Asymmetry suggests smaller negative or null trials were never published, producing exaggerated pooled effects. Heterogeneity is quantified by I squared and Cochran Q, not judged primarily by funnel shape, and reverse causation is a concern of observational designs, not randomized trials.

Reference: Higgins et al, Cochrane Handbook for Systematic Reviews of Interventions, version 6 ed.

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