Identification Screening Eligibility Included Included SEARCH PROCESS 1: CCDAN registers CCDANCTR-STUDIES = CCDANCTR-References = (Unique records) SEARCH PROCESS 2: Other databases Total = SEARCH PROCESS 3: Additional resources (Unique records) Identification SCREENING: no. of records screened after de-duplication 1a = 1b = 2 = 3 = Records excluded: Screening ELIGIBILITY: no. of full-text articles assessed 1a = 1b = 2 = 3 = Eligibility Records excluded: Included INCLUDED STUDIES: no. of studies included in qualitative analysis 1a = 1b = 2 = 3 = Included INCLUDED STUDIES: no. of studies included in meta-analysis