Maartje Boer

CHAPTER 5 146 using longitudinal data. Over time, SMU problems, but not SMU intensity, increased ADHD-symptoms. Specifically, we consistently found that adolescents whose SMU problems increased, also experienced increased attention deficits one year later. Adolescents’ increased SMU problems at T2 also increased impulsivity at T3. Yet, adolescents whose ADHD-symptoms increased neither reported increased SMU intensity one year later nor did they report increased SMU problems one year later. The finding that adolescents’ SMU problems increased ADHD- symptoms one year later, while SMU intensity did not, provides several insights. First, it suggests that the impact of SMU on ADHD-symptoms was not driven by the frequency of use, but rather by the addiction-like aspect of problematic use, such as constant urge to go online or the inability to control SMU. Second, it supports the idea that SMU problems – as defined by substance dependence criteria – have harmful implications, which has been contested in scholarly debates (Kardefelt-Winther et al., 2017; Van Rooij et al., 2018). Previous longitudinal analyses showed that SMU problems, but not SMU intensity, diminished life satisfaction over time (Van den Eijnden et al., 2018). Extending these findings, the present study suggests that SMU problems also increase ADHD-symptoms, whereas SMU intensity does not. Third, the finding that SMU intensity did not increase ADHD-symptoms over time suggests that intensive use of social mediamay be a normative behavior that is integrated into adolescents’ daily lives rather than a problematic behavior. The additional finding that increased SMU intensity did not precede increased SMU problems one year later supports this idea. The longitudinal association between SMU problems and ADHD- symptoms was most pronounced from T2 (2016) to T3 (2017), when increases in SMU problems not only predicted increases in attention deficit, but also increases in impulsivity. This may be because social media platforms became more advanced during this period. For example, Instagram – a social network site for sharing photos through a personal profile – was extended in 2016 with the possibility to share ‘Stories’, which is a series of photos or videos that disappear after 24 hours. Also, Snapchat – a popular instant messenger for sharing photos that disappear after 10 seconds – provided extra incentives for their users from 2016 onwards to use it more intensively, for instance through the launch of ‘Snapstreaks’, which indicate the number of consecutive days users exchanged photos with particular friends (Werning, 2017). The new