Maartje Boer

CHAPTER 9 298 not exclude the possibility that changes in wellbeing may induce changes in SMU problems within shorter time intervals (e.g., month, week, day). After all, the dynamic of behaviors is often dependent on the time scale used to capture the behaviors, which is also referred to as the galloping horse fallacy : A horse’s movement at walking pace is not representative of its movement at galloping pace (Keijsers & Roekel, 2018). Taken together, to paint a more complete picture of the dynamics of the association between SMU behaviors and wellbeing, future longitudinal studies on this association may adopt complementary analytical strategies and study these dynamics within different time frames. Theoretical Implications Adolescents’ SMU has raised concerns among many (Unicef, 2017; Yardi & Bruckman, 2011). In linewith these concerns, several studies showed a negative association between SMU and wellbeing (Frost & Rickwood, 2017; Kelly et al., 2018; Twenge, Martin, et al., 2018). Our finding that this negative relation rather applied to SMU problems, than the intensity of SMU (Key finding 2; Chapters 4-6, 8), nuances this line of research. Recently, several other longitudinal and systematic reviews showed no or only a very small negative average association between adolescents’ SMU intensity and wellbeing (Coyne et al., 2020; George et al., 2020; Meier & Reinecke, 2020; Orben et al., 2019; Piteo & Ward, 2020). Researchers stressed that reports of negative associations were mostly found in cross-sectional work, were particularly representative of earlier decades of research, were driven by analytical decisions (e.g., control variables included), depended on the conceptualization of both SMU and wellbeing, and only applied to specific groups of individuals (Dienlin & Johannes, 2020; Odgers & Jensen, 2020; Orben, 2020a; Orben et al., 2019). Our findings add to this by suggesting that the negative associations between SMU intensity and wellbeing were possibly driven by SMU problems, given that two SMU behaviors were correlated and that the negative relation between the intensity of SMU and wellbeing was often not found (anymore) when taking into account SMU problems (Chapters 5, 6, and 8). Researchers proposed that spending much time on social media threatens adolescents’ wellbeing, for example, because it goes at the expense of meaningful activities (e.g., offline socializing with friends), or because it