Maartje Boer

CHAPTER 9 308 on, for example, depressive symptoms one year later. Although these lagged effects were small, findings showed that at the first measurement occasion, increases inSMUproblems co-occurredwithmoderate increases indepressive symptoms (Chapter 6). Together, these findings imply that, although the effects of SMU problems on these outcomes one year later were small, there may have been a stronger effect that diminished over time. In other words, SMUproblemsmay impact wellbeingmore in the immediate period following increases in SMU problems than one year after increases in SMU problems. In line with this suggestion, it has been argued that digital media use has stronger short-term effects than long-term effects on wellbeing (Dienlin & Johannes, 2020), which relates to the galloping horse fallacy mentioned earlier (Keijsers & Roekel, 2018). To gain more insight into short-term effects of SMU problems, the use of more intensive longitudinal data, such as weekly or monthly measures, is important. Also, the use of experience sampling studies, repeated for several times a year, is considered promising. Through experience sampling, participants report on their thoughts and behaviors several times a day for a short period (e.g., one week), typically through smartphones, which allows researchers to study momentary associations (Beyens, Pouwels, Valkenburg, et al., 2020; Valkenburg, Pouwels, et al., 2021). By repeating experience sampling data collection on SMU problems multiple times per year, it is possible to study the differences between short- and long-term effects, thereby improving the understanding of the effect of SMU problems. The use of more intensive longitudinal data may also enhance current knowledge on the development of SMU problems. In particular, this may allow researchers to capture adolescents’ transitions from normative to at-risk SMU, from at-risk to problematic SMU, as well as the reverse. Our findings showed that adolescents’ levels of SMU problems were rather persistent throughout four years (Chapter 7). Again, this should be interpreted in light of the yearly time intervals that were used for the assessments. There may have been unobserved fluctuations in SMU problems in between the yearly assessments. Furthermore, longitudinal research investigating factors that accelerate adolescents’ transitions from normative to at-risk SMU, and from at-risk to problematic SMU, deepen our understanding of the development of SMU problems. Research on these transitions is considered important, because the