Esther Mertens

16 | Chapter 1 implemented by trained regular school teachers instead of experienced professional facilitators. This elevates the findings from evidence for efficacy to evidence for effectiveness as stated in the “Standards of Evidence” formulated by the Society for Prevention Research (Flay et al., 2005). To evaluate the general effectiveness of universal school-based interventions fostering students’ development in the intra- and/or interpersonal domain, I conducted a meta-analysis. I first examined the overall effectiveness of these interventions in the intrapersonal domain and in the interpersonal domain in general. Second, I analyzed intervention effects on specific competencies and problems within the intrapersonal (i.e., resilience, self-esteem, self-regulation, general wellbeing, and internalizing behavior) and the interpersonal (i.e., sexual health, social competence, school climate, aggression, and bullying) domain. Studying domains in general as well as specific competencies and problems within these domains allowed me to account for the multidimensionality of the general domains (O’Mara, Marsh, Craven, & Debus, 2006). Moreover, it gives a detailed overview of which competencies and problems can currently be successfully affected by universal school-based interventions and which need more attention. Studying intervention effects of universal school-based interventions in general provides the framework to compare the effectiveness of specifically R&W with the effectiveness of school-based interventions in general. Previously, obtained intervention effect were mostly interpreted according to Cohen’s (1988) classification of effect sizes. Recently, researchers are stressing the importance of interpreting effect sizes in relevant contexts such as intervention effects found in previous studies (Durlak, 2009). In order to compare intervention effects in a relevant context, Durlak (2009) proposes three guidelines to take into consideration: 1) quality of the research, 2) comparisons across similar interventions, and 3) practical relevance. I followed these guidelines to establish a relevant context in which I could interpret the intervention effects of R&W obtained in my RCT. That is, in my meta-analysis I took the quality of research (e.g., randomization, type of control group) into account in the calculation of effect sizes when relevant, and I included interventions similar to R&W (e.g., implemented during regular school hours, universal, aim). Practical relevance, the third guideline, is determined by reflecting on the extent to which students’ competencies and problems are meaningfully improved after the intervention. Thus, my meta-analysis not only provides an overview of the effectiveness of universal school-based interventions, it also establishes a relevant context for interpretation of the intervention effects of R&W. Aim 2: Heterogeneity in Contexts and in Population Information regarding under what circumstances (context) and for whom (population) an intervention is effective is not only essential to gain a detailed understanding of the