Evidence-appraisal glossary
Small-study effects
Small-study effects are the tendency for smaller studies in a meta-analysis to report larger or more favorable treatment effects than larger ones. They often show up as asymmetry in a funnel plot.
Also called: small study effect.
Possible causes include publication bias, weaker methods in small trials, or genuine differences in the patients and settings that small studies happen to cover. The key caution is that funnel-plot asymmetry is a signal, not proof of publication bias; the statistical tests for it have low power when only a few studies are pooled, and real differences in study design can produce the same pattern.
This is a plain-language methodology definition for reading research. It is general education, not medical advice.