In a meta-analysis of trials on a new antidepressant, the funnel plot shows marked asymmetry with smaller studies clustered to one side of the pooled estimate. The most likely explanation is:
- A Publication bias with selective reporting of positive small studies ✓
- B Effect modification by trial duration
- C Random error alone, as asymmetry is always due to chance
- D Overestimation of heterogeneity by the I² statistic
Correct answer: A. Publication bias with selective reporting of positive small studies
Explanation
A funnel plot plots study precision against effect size; in its absence of bias it is symmetric around the pooled estimate. Asymmetry with small studies showing exaggerated effects is the classic signature of publication bias or selective outcome reporting, since small negative studies remain unpublished. Effect modification would produce clustering by subgroup rather than by study size, and I² does not determine funnel shape.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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