Inclusion criteria for the review were clearly defined. Several relevant databases were searched. There may have been the potential for language bias as only articles in English were included. Publication bias was assessed, although the meaningfulness of an analysis with fewer than ten trials was limited. Attempts were made to reduce reviewer error and bias during study selection and data extraction, but not for quality assessment.
Quality assessment of included trials indicated that the quality of the evidence base was generally good. Data were combined using meta-analysis, although the exact methods were unclear. Statistical heterogeneity was not detected in any of the analyses.
The authors’ conclusions are based on the evidence and seem reasonable, although the evidence base was small. The authors recommendation for further research appears warranted.