Inclusion criteria for the review were clearly defined. Several relevant databases were searched. There was potential for language bias as only English-language articles were included. Publication bias was not considered and there was no search for unpublished studies, so there was potential for publication bias. The authors did not state how many reviewers undertook study selection, quality assessment and data extraction, which could have introduced error and bias into the review. The included studies had small sample sizes, which the authors acknowledged. Only studies that met RAC quality criteria were included in the analysis, but no details of this assessment were presented and so it was difficult to verify the quality of the included studies. A narrative synthesis was presented, which appeared appropriate, although the synthesis was limited.
Overall, the methodological weaknesses within the review combined with the small sample sizes of the included studies to limit the reliability of the authors’ conclusions, but the authors’ call for further research appeared warranted.