Maartje Boer

CHAPTER 7 200 Declaration of Helsinki and the study procedure was approved by the board of ethics of Utrecht University (FETC16-076 Eijnden). Measures Problematic SMU We used the 9-item Social Media Disorder-Scale to measure problematic SMU, that measures nine symptoms of addiction to social media, including preoccupation, withdrawal, tolerance, persistence, displacement, conflict, deception, escape, and problems (Van den Eijnden et al., 2016). Respondents were asked, for example, whether in the past year they regularly could not think of anything else but the moment to use social media again (i.e., preoccupation), with a dichotomous response scale (1 yes or 0 no ). The scale corresponds to the nine diagnostic criteria for internet gaming disorder according to the appendix of the DSM-5, which also follow a dichotomous response structure (American Psychiatric Association, 2013; Lemmens et al., 2015). A sum-score was computed that denotes the number of present criteria. Higher sum-scores are thereby interpreted as higher levels of problematic SMU. This sum-score followed a Poisson distribution (Figure 7.1), corresponding to the distribution observed in a nationally representative sample of 6,266 Dutch students aged 12 to 16 (Boer, Stevens, Finkenauer, Koning, et al., 2021). Thus, high levels of problematic SMU are rather exceptional in the adolescent population, given that most adolescents do not report any problems, whereas a small minority report many. The scale has been found to provide appopriate criterion validity: The higher the level of problematic SMU, the higher the probability of reporting problems related to mental health, school, and sleep, whereby moderate levels of problematic SMU (i.e., endorsement of two to five problematic SMU criteria) are already indicative of a higher risk of problems (Boer, Stevens, Finkenauer, Koning, et al., 2021). As appropriate for dichotomous variables, reliability was calculated using the tetrachoric correlation matrix (Gadermann et al., 2012), yielding an ordinal alpha ranging from 0.834 to 0.856 at all waves. SMU Frequency Four items assessed respondents’ SMU frequency (Boer, Stevens, et al., 2020).