The review presented a clearly stated research question and the authors' conclusions follow from the results presented. However, there were some limitations. For example, although the review question was clear, the type of participant considered was unspecified and the patient demographic and disease characteristics were not reported. The literature search was restricted to two databases, there was no mention of checking the references of retrieved articles, and no attempt was made to identify unpublished studies. In addition, non-English publications were excluded from the MEDLINE search and were only identified from review articles and the Cochrane database. It is therefore possible that some articles were missed. Publication bias was assessed.
The authors used fairly stringent inclusion criteria for study design but there was no systematic assessment of study quality. It is therefore unclear whether all the studies were of the same quality. The results were pooled appropriately given the evidence of homogeneity. Each of the studies was given a weighting but it is unclear what criteria were used to generate the weighting. While details of the individual studies were presented, the tabulated data could have been more comprehensive.
The authors' conclusions appear to reflect the presented results. However, the findings are not considered in view of the quality of the pooled trials.