Providing a short and effective transdiagnostic treatment intervention and a valid outcome measure for adolescent with anxiety and depression. A randomized controlled trial of the SMART intervention and validation of the CORE-OM in adolescents aged 14 to 17

Anxiety and depression are the most prevalent mental health problems among children and adolescents, and the consequences can be harmful if they are left untreated. Providing short and effective treatment for this group is paramount. When this effectiveness study of The Structured Material for Therapy (SMART) was conducted, it was the first Randomized Controlled Trial (RCT) of short-term transdiagnostic cognitive behavioral therapy (CBT) for adolescents with combined emotional problems, in regular clinical settings in Child and Adolescent Mental Health Services (CAMHS) in Norway. Measures for patients with emotional problems validated in the proper age group are important, both for screening, tracking, providing feedback and documenting outcome for adolescent patients. This thesis investigates the treatment effects in an RCT, of a six-session CBT for emotional disorders in adolescents (14-17 years), and also investigates the long-term effect and change trajectories of anxiety and depressive symptoms, over the course of the SMART treatment and at 6-month follow-up. In addition, we studied the factor structure and psychometric properties of the Clinical Outcomes in Routine Evaluations (CORE-OM) as a transdiagnostic outcome measure for adolescents with emotional disorders. Results from this RCT are promising for youth with emotional problems treated in CAMHS, both at post-treatment and at 6-month follow-up. SMART can be considered as a first step in a stepped care model for treatment of emotional problems in CAMHS. The recovery rates imply that further investigations into the effectiveness of brief treatments should be made. Furthermore, there is a need for more comprehensive second-stage treatments for some of these patients. Finally, the validation of CORE-OM revealed different results than what are reported in adult samples, demonstrating the need for exploring psychometric properties on transdiagnostic instruments used to measure treatment effects in adolescents in CAMHS