Date	Event	Description
15 February 2012	Amended	'Declaration of interest' and 'Contributions of authors' updated; no other changes to text.
15 February 2012	New citation required but conclusions have not changed	Change in listing of authors to include Dr WL van der Pol. This corrects an error in the authorship of this update.
31 March 2011	New citation required but conclusions have not changed	RI Wadman included as new lead author.
8 March 2011	New search has been performed	Databases were searched and review was updated. No new trials were found.
30 July 2008	Amended	Converted to new review format.