This review was withdrawn from The Cochrane Library Issue 3, 2011 because the results are now out-of-date and we realise that the information therein (which has the potential for being used for policy decisions) could be used inappropriately. Please refer to the BMJ article www.bmj.com/content/342/bmj.c7258.full?sid=dc37372f-dde0-455c-8725-dd188f1fba4d for more information. US:
http://onlinelibrary.wiley.com/doi/10.1002/14651858.CD001265.pub3/abstract