The research questions were clear and supported by appropriate inclusion criteria. The authors attempted to identify unpublished studies, but restricted the review to full-text papers and this meant that some relevant studies may have been missed. The authors appeared to take steps to minimise risk of errors and bias during the review process. Although study quality was assessed using the Jadad scale, this was quite limited in its scope and so even though all included studies scored maximum points, the results should be interpreted cautiously (particularly in light of the small sample sizes). Appropriate methods were used to pool the studies. Heterogeneity, publication bias and influence of individual studies were investigated; limited results were presented on these aspects.
Given limited quality assessment and small sample sizes of included studies, the authors' conclusions appear somewhat over-optimistic and should be treated with caution.