The review provided a clear research objective and defined inclusion criteria in terms of population, intervention, comparator, outcome measure and study design. A range of sources were searched for relevant studies and no language restrictions were applied, which reduced the chance that relevant studies were missed. No assessment of the methodological quality of included studies was reported and it was unclear whether measures were taken to minimise error and bias in the review process; therefore, it was not possible to assess the reliability of either the underlying studies or the review process. The use of a fixed-effect model to produce an overall odds ratio was questionable given the degree of between-study heterogeneity indicated by the I2 statistic.
Given the small number of included studies and weaknesses in the review methods and analysis, the authors' conclusions should be viewed cautiously.