The funnel plot of a meta-analysis of small trials shows marked asymmetry, with studies lacking statistically significant effects missing from the region of low statistical precision. The most likely explanation is:

• A Effect modification
• B Publication bias ✓
• C Reverse causation
• D Random misclassification of exposure

Explanation

In a symmetric funnel plot, small imprecise studies scatter widely around the pooled estimate while large studies cluster near it. Asymmetry caused by absence of small nonsignificant studies classically reflects publication bias, since negative small trials are less likely to be submitted and accepted for publication. Effect modification and reverse causation are causal phenomena that cannot be inferred from plot shape, and misclassification would bias results toward the null symmetrically rather than selectively removing studies.

Reference: Cochrane Handbook for Systematic Reviews of Interventions, version 6 ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.