Date	Event	Description
3 January 2013	New citation required but conclusions have not changed	Third update no change to overall conclusions
3 January 2013	New search has been performed	New search, one additional study included (Ho 2012), two studies added to the table of excluded studies (Diekmann 1984, Burke 1998).
23 March 2010	New search has been performed	Second update ‐ risk of bias table added, new search, no new studies identified for inclusion, one study added to the table of excluded studies (Bellingeri 2003), conclusions unchanged.
13 August 2008	Amended	Converted to new review format.
28 November 2007	New search has been performed	First update ‐ for the first update of this review 3 further studies were excluded from the review, no new studies met the inclusion criteria. The conclusions of the review remain unchanged.
12 August 2005	New citation required and conclusions have changed	Substantive amendment This review was first published in the Cochrane Library in issue 4, 2005 with 3 included studies and 9 excluded studies.