Dr. Bhupendrasinh Chauhan reviewed the literature search up to December 2011, identified and reviewed all citations for relevance, reviewed all included trials for methodology and extracted data, entered data, analysed and interpreted results of the meta‐analysis, wrote all version of the manuscript and approved the final manuscript.

Dr. Caroline Chartrand reviewed the protocol, assessed some trial methodology, extracted some data, and approved the final manuscript.

Prof. Francine Ducharme revised and approved the protocol, supervised the selection of trials, reviewed full‐text citations, extracted data and ascertained methodology, contacted all authors or funders to confirm methodology and obtained additional data, interpreted results, edited all versions of the manuscripts and approved the final manuscript.