In a meta-analysis of antipsychotic trials, the funnel plot shows the smaller studies scattered widely but lying almost entirely to one side of the pooled estimate, with a visibly empty corner near the bottom of the plot. The most likely explanation is:
- A Reverse causation in the included observational studies
- B Excessive heterogeneity requiring a random effects model
- C Publication bias favoring positive results ✓
- D Ecological fallacy affecting the pooled estimate
Correct answer: C. Publication bias favoring positive results
Explanation
Small studies carry wide confidence intervals and should scatter symmetrically on both sides of the pooled line if all conducted trials were published. Asymmetry with small negative or null studies missing indicates that such trials went unpublished, producing an inflated pooled effect; Egger's regression test can assess this formally. Heterogeneity widens scatter symmetrically rather than creating a one-sided gap, so it does not explain the pattern described.
Reference: Park's Textbook of Preventive and Social Medicine, 26th ed.
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