Maartje Boer

SMU AND WELLBEING ACROSS COUNTRIES 107 4 met through internet). Therefore, the internal consistency of the items was not assessed (Bollen & Lennox, 1991). Problematic SMU Using the 9-item Social Media Disorder-Scale (Van den Eijnden et al., 2016) respondents indicatedwhether they, in the past year, regularly could not think of anything else but social media (preoccupation), regularly felt dissatisfied because they wanted to spend more time on social media (tolerance), often felt bad when they could not use social media (withdrawal), failed to spend less time on social media (persistence), regularly neglected other activities because of social media (displacement), regularly had arguments with others because of their SMU (problem), regularly lied to parents or friends about their time spent on social media (deception), often used social media to escape from negative feelings (escape), and had serious conflicts with parents or siblings because of their SMU (conflict). Response options were 1 yes and 0 no . Respondents who answered positively to at least six items were classified as 1 problematic user , and the remainder as 0 non-problematic user (Boer, Stevens, Finkenauer, Koning, et al., 2021). Given the dichotomous nature of the items, internal consistency was calculated using the tetrachoric correlation matrix (Gadermann et al., 2012), yielding an alpha of 0.89. Mental Wellbeing Two measures assessed mental wellbeing. Respondents rated their life satisfaction using Cantril’s ladder (Cantril, 1965), ranging from 0 worst possible life to 10 best possible life . The single-item nature of the measure did not allow for assessing internal consistency. However, the measure has been found to provide good test-retest reliability among adolescents (Levin & Currie, 2014). A 4-item subscale from the HBSC Symptom Checklist assessed psychological complaints (Gariepy et al., 2016). Respondents were asked how often in the last six months they experienced feeling low, irritable, nervous, and had difficulties falling asleep. Responses ranged from 1 about every day to 5 rarely or never. Means were computed after items were rescaled. Hence, higher mean scores indicated more psychological complaints. The internal consistency of the items was adequate (Cronbach’s alpha = 0.75).