Funnel plot

Question 1

What are Funnel plots used for?

Answer 1

to demonstrate the existence of publication bias in meta-analyses.

Question 2

Describe how funnel plots are usually drawn i.e. what is found on each axis?

Answer 2

treatment effects on the horizontal axis
study size on the vertical axis.

Question 3

If a funnel plot shows a symmetrical, inverted funnel shape, does this indicate a publication bias is likely or unlikely?

Answer 3

Unlikely

Question 4

What does an asymmetrical funnel plot indicate?

Answer 4

• relationship between treatment effect and study size
  => indicates either publication bias OR
  a systematic difference between smaller and larger studies (‘small study effects’)