In a meta-analysis, the funnel plot of individual study effect sizes against their standard errors is clearly asymmetric, with smaller trials clustered on the side favouring the intervention. The most likely explanation is:

• A Effect modification by baseline severity
• B Overadjustment for prognostic variables in larger studies
• C Random error due to excessive pooling weight of large trials
• D Publication bias with suppression of small negative trials ✓

Explanation

In a funnel plot, precision increases as standard error decreases, so studies scatter symmetrically around the pooled estimate if no bias exists. Asymmetry, especially absence of small studies showing no benefit or harm, is the classic signature of publication bias, since small positive trials get published more easily than small null ones. Egger's regression test can formally assess this asymmetry.

Reference: Park's Textbook of Preventive and Social Medicine, 27th ed.

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Written and medically reviewed by the StethoPrep medical team.