In a meta-analysis of antipsychotic trials, the funnel plot shows that smaller studies cluster asymmetrically to one side of the pooled estimate while larger studies cluster symmetrically around it. The most likely explanation is:
- A Random heterogeneity between studies
- B Reverse causation
- C Publication bias favouring positive small studies ✓
- D Overmatching of controls
Correct answer: C. Publication bias favouring positive small studies
Explanation
A symmetrical inverted funnel shape is expected when estimates scatter randomly around the pooled effect. Asymmetry caused by an absence of small negative studies indicates publication bias or related reporting biases, since small studies are published only when they show striking positive results. Heterogeneity produces wider scatter on both sides, reverse causation is a temporal inference problem, and overmatching is a design issue in case-control studies, none of which produce this pattern.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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