Data extraction and analyses
Data from the trials were extracted by two reviewers (RC and EMB). A standard data extraction form was developed to use for data collection. The following information was system- atically extracted for each of the k randomised trials: characteristics of the study population: age, number of participating females/(males + females)6100% (%F), treatment period (duration time), primary endpoint, intention-to-treat (yes/no), quality score (0–5; as presented above), and body mass index at baseline (inclusion). From each of the k trials (and substudies, if any study reported mutually independent two-group comparisons within the same article), we extracted the following numbers and estimates by group (T, treatment and C, control, respectively): number of patients in the group (n); change in the outcome measure of interest within the treatment group (the mean change, D); SDD in the outcome measure of interest within each group (corresponding to the mean change within the group).
Change scores were used, as some of the studies were small and showed baseline differences in outcome scores between the allocation groups. When the required data in the studies were not presented clearly, a standardised extraction recalculation technique was used, as recommended by The Cochrane Statistical Methods Group.16 To enable the use of meta- regression analyses, the simultaneous mean changes in body weight (%) in each of the two groups per ith substudy (DWeightTi and DWeightCi, respectively) were extracted, together with the SDs of the changes (or calculated assuming the same data distribution as the absolute change, in kg).