Objectives

Sound evaluations of sexual offender treatment are essential for an evidence-based crime policy. However, previous reviews substantially varied in their mean effects and were often based on methodologically weak primary studies. Therefore, the present study contains an update of our meta-analysis in the first issue of this journal (Lösel and Schmucker Journal of Experimental Criminology, 1, 117–146, 2005). It includes more recent primary research and is restricted to comparisons with equivalent treatment and control groups and official measures of recidivism as outcome criteria.

Methods

Applying a detailed search procedure which yielded more than 3000 published and unpublished documents, we identified 29 eligible comparisons containing a total of 4,939 treated and 5,448 untreated sexual offenders. The study effects were integrated using a random effects model and further analyzed with regard to treatment, offender, and methodological characteristics to identify moderator variables.

Results

All eligible comparisons evaluated psychosocial treatment (mainly cognitive behavioral programs). None of the comparisons evaluating organic treatments fulfilled the eligibility criteria. The mean effect size for sexual recidivism was smaller than in our previous meta-analysis but still statistically significant (OR = 1.41, p < .01). This equates to a difference in recidivism of 3.6 percentage points (10.1 % in treated vs. 13.7 % in untreated offenders) and a relative reduction in recidivism of 26.3 %. The significant overall effect was robust against outliers, but contained much heterogeneity. Methodological quality did not significantly influence effect sizes, but there were only a few randomized designs present. Cognitive-behavioral and multi-systemic treatment as well as studies with small samples, medium- to high-risk offenders, more individualized treatment, and good descriptive validity revealed better effects. In contrast to treatment in the community, treatment in prisons did not reveal a significant mean effect, but there were some prison studies with rather positive outcomes.

Conclusions

Although our findings are promising, the evidence basis for sex offender treatment is not yet satisfactory. More randomized trials and high-quality quasi-experiments are needed, particularly outside North America. In addition, there is a clear need of more differentiated process and outcome evaluations that address the questions of what works with whom, in what contexts, under what conditions, with regard to what outcomes, and also why.