In the meta-analysis of a Cochrane-style systematic review, the reviewer plots each trial's effect estimate against its standard error. Small trials scatter widely at the bottom while large trials cluster symmetrically at the top around a pooled value. Marked asymmetry toward one side suggests:
- A Heterogeneity requiring a fixed effects model
- B Publication bias or small-study effects ✓
- C Loss of allocation concealment in large trials
- D Reverse causation
Correct answer: B. Publication bias or small-study effects
Explanation
In a funnel plot, precision increases with sample size, so estimates narrow toward the pooled value as standard error falls. Symmetry implies small negative and positive trials were equally published. Asymmetry indicates smaller studies with particular results were selectively reported, pointing to publication bias, though genuine small-study effects must also be considered. Heterogeneity is assessed by I squared and Cochran Q, allocation concealment relates to individual trial validity, and reverse causation is a causal inference issue unrelated to funnel shape.
Reference: Harrison's Principles of Internal Medicine, 21st ed.
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Written and medically reviewed by the StethoPrep medical team.