What is a funnel plot?

a simple scatter plot of the intervention effect estimates from individual studies against some measure of each study's size or precision

What are Funnel plots used for?

to demonstrate the existence of publication bias in meta-analyses

On a funnel plot what an asymmetrical funnel indicate?

• a relationship between treatment effect and study size
• This indicates either publication bias or a systematic difference between smaller and larger studies ('small study effects')

On a funnel plot what a symmetrical, inverted funnel shape indicate?

that publication bias is unlikely