A funnel plot from a meta-analysis of antidepressant trials is clearly asymmetric, with small studies scattered away from the pooled estimate on the side favouring the drug. The most likely explanation is:
- A Small positive trials were published while small negative trials remained unpublished ✓
- B Large positive trials were suppressed
- C Small negative trials were published more often
- D All included trials had identical sample sizes
Correct answer: A. Small positive trials were published while small negative trials remained unpublished
Explanation
In a symmetric funnel plot, small studies scatter widely around the pooled estimate on both sides. Asymmetry with small studies clustering on the benefit side indicates publication bias: small studies showing significant benefit get published while equally small null or harmful studies stay unpublished. Large trials carry precision and anchor the top of the funnel, so suppression of large positive trials or identical sample sizes does not produce this pattern.
Reference: Systematic Reviews in Health Care: Meta-Analysis in Context (Egger), 2nd ed.
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