Maartje Boer

CHAPTER 6 178 social contact with peers (Boyd, 2014). Moreover, the finding that SMU problems and SMU intensity have differential associations withmental health supports the suggestion that these two types of SMU should be regarded as two separate dimensions of SMU. Our suggestion that adolescents’ high SMU intensity does not impair mentalhealthchallengespreviousresearchthatshowedanegativeassociation between SMU intensity and mental health (Kelly et al., 2018; Riehm et al., 2019; Twenge, Joiner, et al., 2018; Twenge & Campbell, 2018). This discrepancy could be related to the fact that most previous studies on the association between SMU intensity and mental health did not control for SMU problems. The few studies that did so showed that when SMU intensity and SMU problems are studied in one model, only or particularly SMU problems are associated with poor mental health (Boer, Van den Eijnden, et al., 2020; Shensa et al., 2017; Van den Eijnden et al., 2018). Hence, previously found negative associations between SMU intensity and mental health were potentially confounded by unobserved SMU problems . Moreover, the discrepancy may be related to the fact that previous longitudinal studies that showed that high SMU intensity decreased mental health over time were based on analytical approaches that lack separation of within- and between-person variance (Frison & Eggermont, 2017; Riehm et al., 2019; Vannucci & McCauley Ohannessian, 2019). As a result, previously found effects over time were possibly confounded by unobserved time-invariant traits (Hamaker et al., 2015; Orben, 2020a), such as personality. The analysis of the present study controlled for this possibility, which makes results that are inconsistent with previous longitudinal studies plausible (Hamaker et al., 2015). Longitudinal studies that adopted a comparable analytical approach as in the present study showed, in line with our findings, that adolescents’ SMU intensity was not or only weakly associated with poorer mental health (Coyne et al., 2020; George et al., 2020; Houghton et al., 2018; Jensen et al., 2019; Orben et al., 2019). Thus, there is increasing evidence that engaging in high SMU intensity by itself does not impose a risk to adolescents’ mental health. Yet, adolescents who show increased SMU intensity may be vulnerable to other risks, as our findings showed that increased SMU intensity predicted increased SMU problems one year later, although this was only observed from T1 to T2. More research on this potential association, focusing on for