Date	Event	Description
18 August 2008	Amended	Converted to new review format with minor editing.
20 February 2006	New citation required and conclusions have changed	2006, Issue 2: substantive update in which we included one new trial, updated the review authorship, and amended the inclusion criteria to allow only randomized controlled trials (quasi‐randomized controlled trials and observational studies are excluded); no longer contains the description of non randomized studies.