Date	Event	Description
23 November 2016	New citation required but conclusions have not changed	No change to main conclusions.
23 November 2016	New search has been performed	Searches updated, 19 new studies included. 'Summary of findings' table added.
16 July 2008	New search has been performed	Updated for 2008 issue 4 with nine new studies. No changes to conclusions
21 May 2008	Amended	Converted to new review format.
8 February 2005	New citation required but conclusions have not changed	Updated for 2005 Issue 2 with three new studies. No changes to conclusions.
7 April 2002	New citation required but conclusions have not changed	Updated for 2002 Issue 3 with six new studies. No changes to conclusions.