In a systematic review of RCTs, the funnel plot shows asymmetry with studies clustered in the upper-right corner but few small studies with negative results. This pattern MOST suggests:
- A True heterogeneity in the treatment effect
- B Confounding in the included studies
- C Publication bias with small negative trials not published ✓
- D High internal validity of the meta-analysis
Correct answer: C. Publication bias with small negative trials not published
Explanation
Funnel plot asymmetry — specifically, missing small studies with negative or null results — is the classic signature of publication bias, where positive trials are more likely to be published. In the absence of bias, study estimates should scatter symmetrically around the pooled estimate (like an inverted funnel). Trim-and-fill analysis and Egger's regression test are used to quantify this asymmetry statistically.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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