Maartje Boer

SUMMARY AND DISCUSSION 303 9 are of crucial importance for their individual development and everyday functioning (Granic et al., 2020; O’Keeffe et al., 2011; Valkenburg & Peter, 2011). As such, problematizing SMU in general may hinder the understanding of the daily lives of today’s adolescents. In qualitative studies on adolescents’ experiences with their SMU or smartphone use, adolescents reported that they were disappointed that parents and/or teachers primarily expressed their concerns about their screen time instead of trying to understand the importance of SMU in their daily lives (Hjetland et al., 2021; Jameel et al., 2019; O’Reilly, 2020). Nevertheless, it may be important for adolescents and those concerned with their wellbeing to be aware that adolescents’ SMU may become problematic. This is the case when, for example, adolescents experience diminished ability to stop and control SMU, or when SMU is constantly on top of their mind. Especially these behaviors, and not the time spent on or frequency of SMU, may have detrimental effects related to adolescent wellbeing. Given that SMU problems were negatively related to multiple domains of adolescent wellbeing, that this was found across many countries, and that SMU problems were persistent over time (Key findings 2, 3, and 5; Chapters 4-8), schools and/or (government) institutions may consider developing programs aimed at preventing and reducing SMU problems among adolescents. Although the proportion of adolescents reporting problematic SMU (i.e., reporting six to nine symptoms) was low (Chapters 2, 3), such programs may still be relevant, as Chapter 2 showed that about one third of Dutch adolescents reported at-risk SMU (i.e., reporting two to five symptoms). Not only problematic users, but also at-risk users were more likely to experience problems on several important life domains than normative users (i.e., reporting no symptoms or one symptom) (Chapter 2). Researchers using the SMD-scale to study the same three subgroups among a nationally representative sample of Finnish adolescents, showed that, consistent with our findings, at-risk users were more likely to report health complaints, low self-rated health, loneliness, and sleep problems than normative users (Paakkari et al., 2021). Furthermore, our longitudinal study showed that adolescents’ increases in SMU problems predicted subsequent decreases in mental health, regardless of their absolute level of SMU problems (Chapters 5, 6). Together, these findings may warrant the development of prevention and intervention programs on SMU problems among adolescents.