In a meta-analysis, the funnel plot shows small studies scattered asymmetrically to one side, away from the pooled estimate, while large studies cluster symmetrically around it. The most likely explanation for this pattern is:
- A Clinical heterogeneity across included trials
- B Publication bias favoring positive results ✓
- C Random chance variation in effect estimates
- D Effect modification by trial sample size
Correct answer: B. Publication bias favoring positive results
Explanation
A symmetrical inverted funnel shape is expected when estimates scatter randomly around the true effect, with precision increasing as study size grows. Asymmetry, with small studies displaced toward exaggerated effects, is the classic visual signature of publication bias or related small-study effects such as selective reporting and location bias. Small negative or null trials go unpublished, so they never appear on the plot. Heterogeneity produces wider scatter overall, not systematic one-sided displacement tied to study size.
Reference: Gordis Epidemiology, 6th ed.
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