The Influence of Therapist Adherence on Multisystemic Therapy Treatment Outcome for Adolescents with Antisocial Behaviours: A Retrospective Study in Western Australian Families

Multisystemic Therapy (MST) is an intensive family and community-based treatment targeting antisocial behaviours in adolescents. Treatment fidelity has proved crucial for successful implementation of the MST intervention, with prior research demonstrating a strong association with positive and enduring treatment outcomes. The Therapist Adherence Measure (TAM) is a standardised measure reported by caregivers and comprised of 28 items based on the nine treatment principles of MST. Several randomised control trials have confirmed that therapist adherence to the MST model is a valid predictor for a reduction of antisocial behaviours in adolescents. However, there is limited understanding of mechanisms by which therapist model adherence is related to positive changes in family relations and association with decreased adolescent behavioural problems. In this retrospective study, we evaluated effects of therapist adherence on changes in parental factors (e.g., parental mental well-being, monitoring and discipline approach) which in turn were associated with decreased behavioural problems in adolescents. We extracted data collected from 186 families engaged with the MST research program operating within the Western Australian Child and Adolescent Mental Health Service (CAMHS) during 2018–2024. Data for TAMs were collected monthly during treatment, and family outcome measures were collected at pre-treatment and post-treatment. The finding highlights the importance of therapists maintaining treatment fidelity and addressing treatment barriers throughout MST intervention to ensure the desired therapeutic outcomes.