Rapid responses are electronic letters to the editor. They enable our users to debate issues raised in articles published on thebmj.com. Although a selection of rapid responses will be included online and in print as readers' letters, their first appearance online means that they are published articles. If you need the url (web address) of an individual response, perhaps for citation purposes, simply click on the response headline and copy the url from the browser window. Letters are indexed in PubMed.
Probably for the first time on the pages of BMJ the funnel plot is presented
not as a simple triangle, but as a shape recalling the borders of
probability density. This form was introduced by J. Sterne.
Because this small improvement is an important advance in the presentation
and understanding of the data, I believe it is important to acknowledge