The objectives and inclusion criteria of the review were clear. Relevant sources were searched for studies. The search was restricted by language, which risked language bias. It was unclear whether the search was restricted by publication status. Funnel testing was not suggestive of publication bias, but the power of this test is low when applied to so few studies. It was unclear why only short-term outcomes were reported in the review, as reports of long-term follow up were apparently available for some of the included studies. Steps were taken to minimise risks of reviewer bias and error by having more than one reviewer select studies, assess validity and extract data. The process used for validity assessment was not systematically described and some relevant details of study validity were not reported in the review (for example, randomisation and allocation concealment methods), which made it difficult to assess the reliability of study findings. Appropriate statistical techniques were used to combine the studies and assess and explore potential heterogeneity. As the authors noted, the review was limited by the small number of studies and low sample sizes.
Although findings were consistent across studies, the review was limited by the small amount of evidence available and questionable study quality, so the authors’ conclusions may require cautious interpretation.