Does volunteering for sex offender treatment matter? Using propensity score analysis to understand the effects of volunteerism and treatment on recidivism.

A common critique of program evaluations of prison-based sex offender treatment holds that the samples inherently show selection bias because the participants typically volunteer for treatment. To address this critique, we used propensity score analysis to assess the influence of volunteerism on treatment effects. We examined recidivism outcomes for a sample of participants who volunteered for treatment, of whom some participated in treatment (n = 161) and some did not (n = 282) and compared these outcomes to the recidivism rate of a matched sample of nonvolunteers for treatment (n = 443). The primary finding is that offenders who volunteered for treatment did not demonstrate any differences in recidivism rates when matched with and compared to inmates who did not volunteer to participate in treatment. Furthermore, our results revealed that there were a number of significant differences between unmatched volunteers and unmatched nonvolunteers, perhaps most importantly in their risk for future recidivism as measured by the STATIC-99 risk assessment. We discuss study strengths and limitations and present the implications of the findings for policy, practice, and research.