The review addressed a clear question, with well-defined inclusion criteria for intervention, study design and outcomes. Inclusion criteria for participants were not stated. Characteristics of control conditions were not reported, which made it difficult to determine what hypnosis was being evaluated against. Several relevant databases were searched for articles in any language, minimising the risks of language bias. Attempts did not appear to have been made to identify unpublished data, but publication bias was assessed and was deemed unlikely to have influenced the results. Appropriate steps were taken in the validity assessment and data extraction processes to minimise reviewer error and bias. However, it was unclear whether similar steps were taken in the study selection process, so reviewer error and bias could not be definitively ruled out.
A suitable validity assessment was conducted. The quality of included trials was low, partly due to the difficulty in double-blinding hypnotic interventions. Appropriate methods were used to combine the trials. The authors conclusions represent the evidence presented. However, the presence of statistical and clinical heterogeneity between trials limited any conclusions that could be drawn.
In light of the poor quality of available trials, the presence of heterogeneity and the absence of information of comparator conditions, the reliability of the authors' conclusions is unclear.