Maartje Boer

CHAPTER 9 292 intensity was not or to a smaller extent (Chapters 4-6, 8). Furthermore, over time, increases in SMU intensity were not or barely related to subsequent increases in SMU problems and therefore, higher SMU intensity also did not deteriorate wellbeing indirectly through SMU problems (Chapters 5, 6). Together, these findings highlight the importance of considering SMU intensity and SMU problems as associated but different dimensions of SMU: although they are correlated (Chapters 3, 4, 7), they seem to differ with respect to their potential impact on wellbeing. (3) The Association Between Problematic SMU and Wellbeing is Independent of Country Context Findings from Chapters 3 and 4 showed that problematic SMU is a global risk factor, because in all countries it was negatively associated with multiple domains of wellbeing. In contrast, the relation between SMU intensity and wellbeing was more country-context dependent, as positive as well as negative associations were found between higher SMU intensity and indicators of wellbeing across countries (Chapter 4). These findings suggest that the negative relation between problematic SMU and wellbeing is a robust finding and that, worldwide, problematic users face several risks related to wellbeing. (4) Lower Wellbeing Is a Predictor As Well As Outcome of SMU problems, Depending on the Analysis Strategy Our longitudinal chapters investigating directionality showed a unidirectional association between SMU problems and indicators of wellbeing: Within adolescents, increases in SMU problems predicted subsequent increases in ADHD-symptoms and decreases in life satisfaction. Reversely, increases in ADHD-symptoms anddecreases in life satisfactiondidnot predict subsequent increases in SMUproblems (Chapters 5, 6). Nevertheless, we acknowledge that this unidirectional conclusion should be nuanced, because in these chapters we focused on the dynamic of within-person associations. In a subsequent analysis of the same longitudinal data, we focused on between-person differences in wellbeing and their associations with SMU problems over time (Chapter 7). In these analyses, we found that adolescents with higher average