Date	Event	Description
30 November 2014	New search has been performed	Search updated and two trials identified. Methods and risk of bias tables have been updated. A 'Summary of findings' table incorporated for this update
30 November 2014	New citation required but conclusions have not changed	Review updated. One trial included, one trial excluded. Two trials previously excluded are now included (Ledger 1974; Watts 1989)
8 June 2012	Amended	Search updated. Two reports added to Studies awaiting classification (Pietrantoni 1998a; Sweet 1988a).
12 May 2008	Amended	Converted to new review format.
25 January 2007	New search has been performed	Search updated. One new study included (Roy 2003). The conclusions have not changed.
31 January 2004	New search has been performed	Two new studies have been included (Hemsell 1997; Livingston 2003) and one has been excluded (Pastorek 1987b).
30 October 2001	New search has been performed	Eight additional studies were evaluated for inclusion in the review. Six were added to the review and two were excluded. The conclusions drawn from the meta‐analysis were not changed.