Esther Mertens

| 71 Role Personality in School-Based Intervention Personality as a Moderator of Intervention Effects of a School-Based Intervention Personality traits are one of the most influential predictors of psychosocial development, over and above demographic variables and life events (DeNeve & Cooper, 1998; Pellegrino & Hilton, 2012). The important role personality plays in one’s psychosocial development suggests that the effectiveness of interventions aiming to stimulate one’s competencies and prevent the development of problems might be dependent on personality traits. The empirical evidence regarding the role of personality in affecting the effectiveness of interventions is still scarce. By unraveling whether and how personality traits affect intervention effects on both a broad level (i.e., a general domain) and a narrow level (i.e., a specific competence or problem within a general domain), interventions can be tailored to (subgroups of) individuals (Tackett, 2006). In the present study, we examined personality traits as moderators of intervention effects in a universal intervention in which we focused on the intra- and interpersonal domains in general and on specific competencies and problems within these domains. The intrapersonal domain refers to feelings, emotions, and attitudes about the self (Barber, 2005), such as psychological wellbeing and internalizing behavior. The interpersonal domain refers to the ability to build and maintain positive relationships with others and to understand social situations, roles and norms, and respond appropriately (Pellegrino & Hilton, 2012; Shek & Leung, 2016), such as interpersonal relations and aggression. Personality traits influence the extent to which individuals are likely to develop problems, which in turn may affect intervention effects. The vulnerability theory (Tackett, 2006) states that certain personality traits can increase one’s risk of developing and maintaining problems in the intra- and interpersonal domains. Particularly in the intrapersonal domain, personality traits seem important predictors of one’s competencies and problems (Van Leeuwen, Mervielde, Braet, & Bosmans, 2004). Individuals who have low levels of Extraversion, Agreeableness, or Conscientiousness, or high levels of Neuroticism, or a combination of these, are suggested to be more vulnerable to develop problems (Tackett, 2006). These individuals tend to be oriented towards their inner world of subjective experiences (low levels of Extraversion), ruthless and manipulative (low levels of Agreeableness), show difficulties in delaying gratification and modulating impulsivity (low levels of Conscientiousness), and/or perceive the world as distressing or threatening (high levels of Neuroticism; Pellegrino & Hilton, 2012; Shiner & Caspi, 2003). Furthermore, these levels of personality traits 4