The review addressed a clear question and was supported by reproducible eligibility criteria. The restriction to searching only for studies published in English meant that some relevant studies may have been missed, and the review results appear to have been subject to publication bias. Duplicate processes were employed to reduce the risks of reviewer error and bias during data extraction, but the authors did not report on whether such methods were used to select studies or assess study quality.
Adequate primary study details were provided. Study quality was assessed, but it was unclear how well the criteria translated into an evaluation of whether individual trial results were reliable, as minimal method and result details were presented. It was therefore unclear how reliable the results of 'good' studies were.
The value of the pooled estimates appears questionable since a fixed-effect model was used, despite the presence of considerable heterogeneity. Appropriate methods were used to assess and investigate heterogeneity. However, statistically significant heterogeneity was present not only in the main analysis, but also in many of the subgroup analyses; there was also evidence that significant publication bias had affected the results. Furthermore, the authors noted uncertainty regarding whether the treatment effects found were clinically-relevant effects. Although some of these issues were discussed, they were not incorporated into the overall conclusions.
Limitations of the review cast considerable doubt on the reliability of the authors' conclusions, which appear over-optimistic.