Maartje Boer

CHAPTER 1 18 indicators of wellbeing, in particular mental health (i.e., ADHD-symptoms, depression symptoms, life satisfaction), when studying associations with SMU behaviors, further advances current knowledge. This namely reveals which aspect of wellbeing is (most) vulnerable to high SMU intensity and/ or SMU problems and, reversely, which aspect of wellbeing (mostly) explains high SMU intensity and/or SMU problems. How Do SMU Problems Develop Over Time? Problematicbehaviorsaretypicallynotstatic,but, instead, showdevelopmental trajectories depending on age or other biological, social, and cognitive developments. So far, it is unknown how SMU problems develop over time throughout adolescence. Research on deviant behaviors and mental health problems, such as aggression, delinquency, binge drinking, and depression, show that these behaviors typically develop through multiple trajectories throughout adolescence, including a persistently low, persistently high, and one or more variable trajectories (Bongers et al., 2004; Chassin et al., 2002; Dekker et al., 2007; Reinecke, 2006b). Considering SMU problems as deviant behaviors that are related to mental health problems, SMU problems may develop through comparable trajectories. So far, this has been unexplored. In addition, it has been put forward that adolescents with low mental health and poor social competencies are more likely to report SMU problems, because of their limited ability to regulate their SMU or because they prefer online interaction over face-to-face encounters due to their psychosocial vulnerabilities (Caplan, 2003; Davis, 2001; Mérelle et al., 2017; Wu et al., 2013). However, it is unclear whether these vulnerabilities increase the risk of, for example, temporarily or persistently high levels of SMU problems. Given the increasing evidence that SMU problems threaten adolescents’ wellbeing (Marino et al., 2018b; Van den Eijnden et al., 2018), it is important to identify whether, when, and for whom SMU problems increase, decrease, or persist over time. Not only does this information advance current theory on SMU problems by identifying the course of the behavior; it also allows researchers to identify in which period of adolescence and to whom prevention and intervention programs on problematic SMU may be most valuable. Furthermore, to enhance our understanding on (the development) of SMU problems even more, trajectories of adolescents’ SMU problems