Date	Event	Description
4 August 2008	New search has been performed	For the first update, published in Issue 4, 2008, the following changes were made: (1) the search was updated to June 2008, which resulted in the identification of no new studies; (2) the 'Synopsis' was converted to a 'Plain language summary'; (3) methodological quality assessment scores were no longer totalled; (4) some reformatting of the review and completion of one formerly incomplete table. There were no changes made to the conclusions.
10 July 2008	Amended	Converted to new review format.
16 May 2005	New citation required and conclusions have changed	First version of the review.