Analysis
All analyses were performed using STATA 14.012. We have reported results of both fixed and random effects meta-analysis.
Where some summary data were missing for the reported trial results, we have imputed missing information (e.g. standard deviations or intra-cluster correlation coefficients (ICCs)) using other information in the trial paper or values from similar trials13. Sensitivity to imputed values was assessed by imputing a range of different values.
Where the reported outcome data were from either an individually randomised trial or a cluster trial where the results had already been adjusted for clustering by the unit of randomisation, the standard errors were utilised without adjustment. Where adjustment for clustering was required the standard error was multiplied by the square root of the design effect (DE); this requires the average cluster size (M) and the intra-class correlation coefficient (ICC)13.
\(DE=\) 1+(M-1)ICC
Where possible we report the I2 statistic as a measure of heterogeneity 13. The I² statistic estimates the percentage of variation across studies that is due to study heterogeneity rather than chance.