Data were extracted independently from included papers by at least two reviewers.
Authors of trials were contacted for additional and missing data.
Relative risks (RR) and 95% confidence intervals (CI) of homogeneous dichotomous data were calculated.
A random effects model was used for heterogeneous dichotomous data.
Where possible the numbers needed to treat (NNT) were also calculated.
Weighted or standardised means were calculated for continuous data.