Mental health diversion and criminal justice outcomes: a population-based cohort study of 53,605 justice-involved adolescents

Incarceration of adolescents is associated with a range of adverse outcomes, yet high-quality evidence comparing its effectiveness to non-custodial alternatives is limited. We compared mental health diversion, community-based legal orders, and custodial sentencing in reducing reoffending among justice-involved adolescents. We conducted a population-based retrospective cohort study using linked health and justice records from New South Wales, Australia, including all adolescents aged 10 to 17 years with a conviction between an index court finalization between 2 July 2001 and 24 December 2020. The primary outcome was first proven reoffending within 12 months following first court finalization in adolescence. Among 53,605 justice-involved adolescents, 2,171 (4.0%) received mental health diversion, 44,887 (83.8%) community orders, and 6,547 (12.2%) custodial sentences. Standardized any-reoffending risk was 47.2% under diversion, 56.6% under community orders, and 64.5% under custody. Diversion was associated with an absolute risk difference of − 17.7% points compared with custody (95% CI − 23.2 to − 12.1) and − 9.9% points compared with community orders (95% CI − 14.9 to − 4.1). The risk difference for community orders compared with custody was − 7.8% points (95% CI − 12.8 to − 3.3). Reduction in reoffending under diversion were greatest among adolescents with disruptive behavioural disorders (− 26.5% points, 95% CI − 34.9 to − 18.3), mood disorders (− 22.9% points, 95% CI − 37.2 to − 6.4), and intellectual disability (− 38.0% points compared with community orders, 95% CI − 60.0 to − 14.5). Mental health diversion and community orders reduced reoffending risk compared with custody. Effects were greatest among adolescents with disruptive behavioural disorders, mood disorders, and intellectual disability. These findings support the use of non-custodial sentencing for justice-involved adolescents with mental health disorders and indicate that those with neurodevelopmental and externalizing presentations may benefit most.