Aim: To investigate whether referral to the Intensive Drug and Alcohol Treatment Program (IDATP) reduces re‑offending and/or returns to custody.

Method: The study sample included 1,285 offenders who were released from NSW custody on or after 1 January 2013, all of whom satisfied IDATP eligibility criteria. An intention-to-treat (ITT) design was employed to protect against unobservable selection bias in program commencement and completion, with the treatment group comprising the complete sub-sample of 340 offenders who were referred to IDATP (59.4% of whom commenced treatment). Propensity score matching is used to construct matched samples of treated and untreated offenders across a range of observable characteristics related to recidivism risk. Separate matchings were constructed for offenders with follow‑up periods of 3, 6, and 12 months. Rates of re‑offending and/or return to custody were compared for the matched samples of treated and untreated offenders.

Results: IDATP referrals were younger than the similarly eligible offenders in the comparison group, had a more extensive criminal history, and had been classified according to official risk assessment measures as being at higher risk of recidivism including for reasons related to their drug and/or alcohol use. Nonetheless, after matching on the estimated propensity score, the samples of offenders were similar across these and a broader range of observable characteristics. Although rates of re‑offending and/or return‑to‑custody were lower for the matched treatment than matched comparison group at follow-up periods of 6 and 12 months, there was no statistically significant difference in recidivism outcomes.

Conclusion: The power of the statistical analyses was severely limited by the small sample of IDATP participants and the ITT research design. The power to detect a treatment impact will improve as more offenders engage with IDATP over time.