Intended for healthcare professionals

Rapid response to:

Education And Debate

Forest plots: trying to see the wood and the trees

BMJ 2001; 322 doi: https://doi.org/10.1136/bmj.322.7300.1479 (Published 16 June 2001) Cite this as: BMJ 2001;322:1479

Rapid Response:

Are funnel plots now the technique of choice?

Reading this article on forest plots gave me a feeling of deja-
vu(1).A quick electronic search of past BMJs was rewarded by a paper on
funnel plots in 1997.(2) Funnel plots appear to be very similar to forest
plots.
Funnel plots are plots of effect estimates against sample size, and may
have an advantage over forest plots both visually and statistically.
Visual interpretation of a funnel plot is immediate, asymmetry of the
chart suggesting bias in the studies selected, and this can be further
explored by statisical analysis.
It has been suggested that funnel plots should be used routinely to
examine for the likely presence or absence of bias.(3)
Funnel plots were not mentioned in this article, but do the authors agree
that this is now the technique of choice in the display of results of meta
-analysis for the detection of possible bias?

(1) Lewis S, Clarke M. Forest plots:trying to see the wood and the
trees BMJ2001;322:1479-80

(2)M, Davey Smith G, Schneider M, Minder CE. Bias in meta-analysis
detected by a simple, graphical test. BMJ1997;315:629-34

(3)Egger M,Davey Smith G, Meta-analysis bias in location and
selection of studies BMJ1998;316:61-66

Competing interests: No competing interests

21 June 2001
Robert Fleetcroft
general practitioner
Great Yarmouth Primary Care Trust