MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials (CENTRAL), Cochrane Database of Systematic Reviews, ACP Journal Club, DARE, PREMEDLINE, OLDMEDLINE, CINAHL, BIOSIS Previews, LILACS, KOREAMED, SAMED, IndMED, SIGLE, ScienceDirect and Ingenta Connect databases were searched up to January 2005. No language restrictions were applied. Reference lists of relevant reviews and identified articles were checked for additional studies. Search terms were reported.