We identified relevant studies meeting the inclusion criteria by a computer-aided search of CENTRAL in the Cochrane Library (Issue 3, 2012), MEDLINE (from 1966 to February 2012), SCOPUS and CINAHL (from 1982) by using both free text and MeSH terms. We also searched Proquest Dissertations, Open SIGLE and Persian medical databases (Iranmedex, Irandoc). Studies were eligible regardless of time of publication, language of publication, or publication status. For MEDLINE search strategy see online Appendix 1.