Date	Event	Description
26 February 2011	New search has been performed	New searches, no new studies included, two studies added to the Table of Excluded studies (Lo 2010; Lo 2010a). The review's conclusions remain unchanged.
9 November 2010	Amended	Contact details updated.
16 March 2010	Amended	Contact details updated.
13 May 2009	Amended	Contact details updated.
21 January 2009	New search has been performed	First update of review no new studies identified, conclusions remain unchanged.
5 August 2008	Amended	Converted to new review format.
26 November 2006	New citation required and conclusions have changed	Substantive amendment