Inclusion criteria for the review were broadly defined and several relevant databases were searched for articles in any language. There may have been the potential for publication bias, as the authors did not state whether unpublished studies were considered; publication bias was not assessed. The authors did not state how many reviewers performed study, data extraction and quality assessment, but did state that the CHERG guidelines were followed, which should have minimised error and bias in the review.
The quality assessment indicated the variable quality of the included trials, which the authors acknowledged. Trials were combined using meta-analysis; heterogeneity was explored but was not reported.
Overall, the review had some methodological problems, but the authors' conclusions were based on the evidence and appear reasonable.