Maartje Boer

SUMMARY AND DISCUSSION 293 9 levels of ADHD-symptoms and lower average levels of life satisfaction were more likely to show higher levels of SMU problems over time than adolescents with lower average levels of ADHD symptoms and higher average levels of life satisfaction. Together, although changes in wellbeing within adolescents were not associated with subsequent changes in SMU problems within adolescents (Chapters 5, 6), adolescents with lower wellbeing relative to other adolescents were more likely to report higher levels of SMU problems over time (Chapter 7). Conceptually, these findings suggest that stable individual differences in adolescents’ wellbeing at the between-person level affect their susceptibility to SMU problems, whereas temporal fluctuations in wellbeing at the within-person level are not predictive of SMU problems. (5) SMU Problems Are Persistent Over Time Chapter 7 identified four trajectories of SMU problems, whichwere, in general, persistent over time. More specifically, two trajectories showed relatively high levels of SMU problems that remained high over time, suggesting that problematic SMU is not a behavior that desists naturally. In addition, two trajectories showed persistently low levels of SMU problems. These findings are consistent with the finding that, on average, adolescents did not show a linear change in SMU problems over time (Chapters 6 and 8). (6) The Association Between SMU Intensity and Wellbeing Can Be Positive or Negative, Depending on Individual Characteristics, Country Context, and Wellbeing Domain Although our longitudinal study showed that higher SMU intensity was, on average, not associated with wellbeing (Chapters 5, 6, 8), in some cases higher SMU intensity was related to lower levels of wellbeing, in other cases it was related with higher levels of wellbeing, or it was not related to wellbeing at all. More specifically, for some adolescents, increases in SMU intensity were associated with increases in life satisfaction, whereas for others, increases in SMU intensity were associated with decreases in life satisfaction, although the study did not identify which individual characteristics explained these differences (Chapter 8). Our findings also suggest that country contexts matters, given that