Maartje Boer

CHAPTER 5 134 are in line with criteria for substance dependence . Adolescents were asked “During the past year, have you (…)”, followed by, for example, “regularly had no interest in hobbies or other activities because you would rather use social media?”, which refers to the criterion ‘displacement’. Respondents replied on a dichotomous scale (1 = yes and 0 = no ). High values on the scale indicated a high level of SMU problems. Factor loadings ranged between 0.52 and 0.85 across all three waves. Prior validation research showed that the SMD-scale had medium to large positive correlations with compulsive internet use and self-declared social media addiction, confirming adequate convergent validity (Van den Eijnden et al., 2016). The scale was also found to have small to moderate positive correlations with mental health problems and frequency of SMU, confirming satisfactory criterion validity (Van den Eijnden et al., 2016). Given the dichotomous nature of the items, internal consistency was calculated using the ordinal alpha that is based on the tetrachoric correlation matrix (Gadermann et al., 2012). Ordinal alpha values were 0.83 (T1), 0.90 (T2), and 0.89 (T3). ADHD-Symptoms The ADHD-Questionnaire was selected for use in this study, as it has been shown to be a reliable and valid measure of ADHD-symptoms in adolescent populations (Scholte & Van der Ploeg, 1999). In order to gain insight into which ADHD-symptoms related to social media behaviors, the three symptoms of ADHD were measured separately. Attention deficits was measured using nine items, for example “I avoid tasks that require prolonged effort”. Factor loadings ranged between 0.60 and 0.79; Cronbach’s α values were 0.89 (T1), 0.90 (T2) and 0.87 (T3). Impulsivity was indicated by six items, such as “I find it difficult to wait for my turn”. Factor loadings ranged between 0.55 and 0.77; Cronbach’s α values were 0.79 (T1), 0.83 (T2), and 0.81 (T3). Six items were used to measure hyperactivity , for example “I feel restless”. Factor loadings ranged between 0.47 and0.85; Cronbach’s α valueswere 0.85 (T1), 0.88 (T2), and0.82 (T3). Respondents replied on five-point response scales, where high values indicated higher levels of ADHD-symptoms (1 = never and 5 = very often ). Measurement Invariance Over Time To draw conclusions on effects over time, identical constructs should be