40 Chapter 2 11 treatment centers met these criteria, and they were assigned to either the intervention or control condition (see Figure 1). Participants in the intervention condition attended Take it Personal! in eight groups of three to four adolescents. The average (and median) cluster size was seven participants per treatment center (ranging from 2 to 14 per treatment center). Figure 1 Flow diagram of enrolment and retention by treatment arm Note. ITT = Intention to treat. 2.3 Procedure Treatment centers were informed about the prevention program and were invited to participate in this study. Adolescents who were found to be eligible to participate by the researcher, were then approached by their care-giver or clinician who invited them to participate. Upon registration, adolescents were pre-screened. Gender and date of birth were registered using self-reported questionnaires (see Outcome measures). The questionnaires included pictograms and images administered via a web-application on a tablet computer that adolescents operated themselves. A researcher read every question aloud and, if necessary, provided further clarification with simple wording. An adolescent’s personality profile (SS,
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