Using a predefined data extraction form we extracted data from the included trials on journal, sample size, patient population, type of intervention (drug, medical device, surgical procedure, health promotion activity, other therapeutic intervention 32), duration of follow-up, centre status (single or multicentre), and sponsor (for profit, not for profit, or mixed 33).
Two authors (MJS and JHJ) performed the data extraction and quality assessment using a predefined data extraction form.
Disagreements between reviewers on study quality were resolved by discussion between the three reviewers.> Data were extracted by using a predefined data extraction form regarding study population, design, setting, outcome measures, prognostic factors and strength of association.
Three authors (KRM, TB and MD) independently extracted data from included reviews using a predefined data extraction sheet.
Data extraction was performed by 1 reviewer and checked by a second reviewer using a predefined data extraction form.
The first author (GS) extracted data on the 12 included studies using a predefined data extraction table, informed by the Centre for Reviews and Dissemination guidelines 27 and National Institute for Health and Care Excellence NICEE) 28 (see online supplementary appendix 1).
The data extraction and quality assessment were conducted by three authors (JAL, MJS and JHJ) using a predefined data extraction form.
The data extraction and quality assessment will be conducted by three authors (JAL, MJS and JHJ) using a predefined data extraction form.
Two independent investigators (ED and EA) extracted descriptive, methodological and outcome data from all eligible studies using a predefined data extraction form.
