Maartje Boer

THE COMPLEX ASSOCIATION BETWEEN SMU AND WELLBEING 241 8 The high dropout rate in T4wasmainly due to dropout of entire pre-vocational schools, school years, and school classes, for example because the survey assessment could not be scheduled due to practical constraints. Hence, the dropout was not related to individual selection. Parents of participating adolescents were provided with the opportunity to refuse participation of their child. Adolescents were informed that their participation was anonymous and voluntary, and that they could withdraw their participation at any time. The survey assessment took place in the classroom setting through digital self-completion under supervision of research assistants. The assessments were carried out in accordance with the Declaration of Helsinki and approved by the board of ethics of Utrecht University (FETC16-076 Eijnden). Measures Life Satisfaction Life satisfaction was measured using the 7-item Student’s Life Satisfaction Scale (Huebner, 1991). Respondents were asked about their thoughts around their own life, for example: ‘My life is going well’ and ‘I have what I want in life’. Response options ranged from (1) strongly disagree to (6) strongly agree. A mean score was computed that denoted adolescents’ life satisfaction. Cronbach’s alpha was 0.83. SMU Intensity We distinguished four SNS and two IM activities, each measured with one item (Van den Eijnden et al., 2018). SNS intensity was indicated by SNS viewing (‘How many times per day do you view social network sites?’), SNS posting (‘How many times per week do you post a message, photo, or video on social network sites?’), SNS liking (‘Howmany times per week do you ‘like’ messages, photos, or videos of others on social network sites?’), and SNS responding (‘How many times per week do you respond to messages, photos, or videos on social network sites?’). Response options ranged from (1) never or less than once to (7) more than 40 times . The questionnaire presented examples of SNS including ‘Facebook, Twitter, Instagram, Google+, or Pinterest, but not WhatsApp or SnapChat’. Regarding IM intensity, we assessed IM viewing