In a funnel plot from a meta-analysis, studies with small sample sizes and large effect sizes cluster to one side of the plot, leaving an asymmetric appearance. This pattern most directly suggests:
- A Genuine heterogeneity of effect sizes
- B High between-study variance due to random-effects
- C Publication bias favouring positive results ✓
- D Berkson's bias in individual studies
Correct answer: C. Publication bias favouring positive results
Explanation
An asymmetric funnel plot with missing studies in the lower-left corner (small studies with null or negative results) strongly suggests publication bias, because small studies with non-significant results are less likely to be published. The Egger test and Begg test are used to formally test funnel plot asymmetry. Genuine heterogeneity creates scatter throughout the funnel symmetrically. Random-effects modelling widens confidence intervals but does not alter funnel shape.
Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.
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