Sustainability of the effectiveness of a programme of multisystemic treatment (MST) across participant groups in the second year of operation

In order to examine the sustainability of programme effectiveness, we investigated whether the effects of multisystemic treatment (MST) on a second group of adolescents would match those reported in an earlier randomised controlled trial (RCT). Pre‐ and post‐treatment assessments were analysed in a participant group of 105; 55 youths were referred to MST in the programme's second year of operation (MST2), and 50 youths were included in the RCT the first year in which 30 were randomly assigned to MST (MST1) and 20 to regular services (RS).At two project sites, MST clinical outcomes in the second year of programme operation matched and, for key indices of anti‐social behaviour, surpassed those achieved during the first year. In addition the MST treatment delivered in the second year was more effective than regular child welfare services in preventing out of home placement and reducing internalising and externalising behaviour. Together, these results demonstrated sustained effectiveness of the programme as well as indication of programme maturation effects. No group differences were registered for social competence. MST youths treated in the second year were significantly younger than those referred to treatment in the first year (MST1) but age had no moderating effect on the outcomes.