Date	Event	Description
6 June 2013	New citation required but conclusions have not changed	New search carried out. New author joined the review team. One new study included, four previously excluded studies now included. One new study excluded. Risk of bias assessed for all included studies and text updated. No change to conclusions.
6 June 2013	New search has been performed	One new study included, four previously excluded studies now included. One new study excluded.
11 November 2009	Amended	Some graph labels changed and minor edits made to the text.
3 November 2008	Amended	Converted to new review format.
12 November 2007	New search has been performed	Four additional excluded studies added. Dates of searches updated. Plain Lanugage Summary provided by the Cochrane Consumer Network added and edited by author. Minor copy edits throughout text.. Analyses graphs copy edited for uniformity in presentation. Technical edits performed to clarify outcome statistics. Conclusions remain unchanged.