2 41 The effectiveness of Take it Personal! on substance use IMP, AS or NT) was determined according to the highest score on the Substance Use Risk Profile Scale (SURPS; Woicik et al., 2009). If more than one high-risk personality profile was identified in one adolescent, the independent researcher contacted that adolescent’s clinician and appealed to his/her clinical experience to determine the profile that explained the adolescent’s substance use the most clearly. In addition, case files were used to collect information about IQ (measured with the WAIS or WISC). These files include recent and relevant information concerning the client (never older than approximately two years). An independent researcher assigned adolescents to either intervention or control condition based on participants’ numbers, their treatment center and their personality profile. Individual or cluster randomization was not possible due to the number of available treatment centers, participants and the fact that the prevention program required a group of three or four adolescents with the same personality profile. Furthermore, groups were comprised of adolescents who were already receiving treatment in the same treatment center. This was done to lower the threshold for participation, as traveling between treatment centers on a weekly basis would cause too much inconvenience for adolescents and care professionals. Hence, in practice, adolescents within the same treatment center were assigned either to the control condition or to the intervention condition. Adolescents and parents (or legal representatives) were informed that the intervention was designed to reduce problems with alcohol and drug use and that their data would be processed anonymously. For each measurement, the participants received a €5 gift card. Data was collected between Januarfy 2015 and April 2017. Both adolescents and parents provided active informed consent. The Ethics Committee of Radboud University approved this study (ECSW2015–0903-303), and the trial was registered at the Dutch Trial Register (NTR5037; 15 April 2015). 2.3.1 Take it Personal! The prevention program Take it Personal! comprised five 45-minute group sessions and five 30-minute individual sessions, conducted within a 6-week time-span. For each of the four personality profiles (SS, IMP, AS and NT), specific interventions were developed that were structurally the same but contained different personalityspecific materials, games and (psychomotor therapy) exercises. Trainers were one psychologist and one psychomotor therapist from the participant’s own treatment center, who had received specific training on Take it Personal! prior to the start of the study. This training included practice in motivational interviewing, cognitive behavioral therapy, and information on the theoretical background of the program. Both trainers conducted the group sessions together, and for the individual sessions
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