What works seeks to identify rehabilitative treatments which are successful in reducing the likelihood that offenders will reoffend. A large number of small case–control studies have been reported in the literature, but with conflicting results. Meta-analysis has been used to reconcile these findings, but again with conflicting results. We reanalyse one of the published meta-analyses in the corrections literature and argue the importance of specifically modelling heterogeneity and selection bias. A sensitivity approach is advocated, suggesting lower average effects and substantially increased measures of uncertainty. The method is tested on a medical example where independent confirmation from a large controlled trial is also available.