Date	Event	Description
26 April 2017	New citation required but conclusions have not changed	This update includes nine new studies. The total number of included studies in the review is now 18. New review authors have contributed to this update. We have excluded from this update seven studies previously included in the review (3 controlled before‐after studies, 3 non‐randomised trials, and 1 study focussing on mental health problems).
26 April 2017	New search has been performed	This is the first update of the Cochrane review published in 2005. We have conducted a new search and have updated other content. We updated the search in March 2017 and added one trial report to ‘Studies awaiting classification’.
16 July 2004	New citation required and conclusions have changed	We have made substantive amendments.