D a t a s o u r c e s Studies were identified by searching MEDLINE, the Cochrane Central Register of Controlled Trials, EMBASE/Excerpta Medica, Web of Science, National Library of Medicine Gateway, Cardiosource, the Clinical Trials Registry, Clinicaltrials.gov, CRISP, the National Research Register, the GlaxoWellcome Clinical Trials Register, LILACS, OCLC ProceedingsFirst, and the National Heal...