What Is a Funnel Plot?
Looking for the full method? Read the detailed guide: How to Interpret a Funnel Plot.
A funnel plot is a scatter plot used in meta-analysis, plotting each study's effect estimate against a measure of its precision. Without bias, it should look like a symmetrical inverted funnel around the pooled estimate.
Example
Invented for teaching: If small studies with null or unfavourable results are missing, the lower part of the plot appears lopsided, which may suggest small-study effects or publication bias.
Common misunderstanding
Asymmetry does not prove publication bias; heterogeneity, poor methods in small studies, or chance can also cause it. Tests and visual inspection are unreliable with fewer than about 10 studies.
Learn more
See How to Interpret a Funnel Plot.
References and further reading
- Sterne JAC, Sutton AJ, Ioannidis JPA, et al. Recommendations for examining and interpreting funnel plot asymmetry in meta-analyses of randomised controlled trials. BMJ. 2011;343:d4002. doi:10.1136/bmj.d4002
- Egger M, Davey Smith G, Schneider M, Minder C. Bias in meta-analysis detected by a simple, graphical test. BMJ. 1997;315:629-634. doi:10.1136/bmj.315.7109.629
Related reading
This page is general educational information about research methods. It is not medical, legal or regulatory advice; follow your institution's ethics board and your target journal's instructions.