Date	Event	Description
8 February 2011	Amended	Contact details updated.
24 September 2010	Amended	Contact details updated.
4 July 2010	Amended	Contact details updated.
13 May 2009	Amended	Contact details updated.
28 May 2008	Amended	Converted to new review format.
15 January 2008	New search has been performed	Review updated ‐ studies sought but none found
15 January 2008	New citation required but conclusions have not changed	Further studies satisfying our inclusion criteria were sought in MEDLINE (via Ovid), EMBASE (via Ovid) and Cochrane CENTRAL to December 2007. No further studies were identified, so the conclusions of the review are unchanged.
30 December 1999	New citation required and conclusions have changed	Substantive amendment