Maartje Boer

SMU AND ADHD-SYMPTOMS 147 5 affordances may havemade social media evenmore attractive to adolescents and made them harder to resist. These changes may tax adolescents’ self- control more heavily, in turn increasing ADHD-symptoms. We did not find support for our proposition that adolescents with more ADHD-symptoms would be particularly attracted to the features of social media. Although adolescents with more ADHD-symptoms are sensitive to developing addiction-like behaviors, such as substance dependence (Ohlmeier et al., 2008), we did not observe this sensitivity for the development of SMU problems. Social media are possibly more salient in the daily lives of adolescents than substances. Therefore, SMU problems may be different in their etiology from substance dependence. Alternatively, our study design and method might have prevented us from observing an effect of ADHD- symptoms on socialmediabehaviors. Specifically, ADHD-symptomsmay have affected social media behaviors at a younger age, not included in our study. Furthermore, the measurement occasions were a year apart, while behaviors may influence each other within a shorter time interval. Also, adolescents’ initial level of ADHD-symptoms at the between-person level (e.g., genetically determined) may have influenced changes in social media behaviors. The within-person oriented study design of the RI-CLPM does not eliminate the possibility that stable levels of ADHD-symptoms at the between-person level affected social media behaviors over time. An additional finding was that adolescents who experienced increased SMU problems were likely to experience increased SMU problems one year later as well, with high effect sizes. Scholars have questioned whether SMU problems, indicated by symptoms of addiction, reflect actual behavioral addiction symptoms. They have put forward that the behavior should lead to significant impairment, and that it should persist over time (Kardefelt- Winther et al., 2017). The finding that SMUproblems have harmful implications over time, and that they are highly likely to persist over time, supports the suggestion that SMU problems, as defined in this study, reflect behavioral addiction symptoms. Strengths, Limitations and Future Directions The present study has important strengths related to the research design. By disentangling within- and between-person effects, we controlled for all