Maartje Boer

CHAPTER 4 106 adolescents from 47 countries/regions. Countries were excluded from the present study when individual-level data on SMU ( n countries = 3) or country- level data on mobile internet accessibility were unavailable ( n countries = 13), or when data were not submitted by the time of current analyses ( n countries = 2). Adolescents who responded that the SMU questions did not apply to them were also excluded ( n individuals = 6,174). The analysis sample consisted of 154,981 adolescents within 29 countries/regions (51% girls, M age = 13.54; SD age = 1.61). Sampling methods (schools or classes as primary sampling units), data collection procedures, and questionnaires were standardized and strictly followed the HBSC international research protocol (Inchley et al., 2018). Before the survey assessments, in each country, researchers translated the English survey questions into the respective national language. Subsequently, different researchers back-translated the survey questions to English without prior knowledge of the original English survey questions. Next, language experts within the HBSC network compared the original and back-translated English survey questions. Detected inconsistencies were corrected in the national language surveys to ensure comparability of findings across different languages and cultural settings (Inchley et al., 2018). Institutional ethical consent was sought in each participating country. Participation was voluntary and anonymous, and consent was obtained from adolescents, parents, and schools. Individual-Level Measures Intense SMU Using four items adapted from the EU Kids Online Survey (Mascheroni & Ólafsson, 2014), respondents were asked how often they have online contact through social media with close friends, friends from a larger friend group, friends that they met through the internet, and other people (e.g., parents, siblings, classmates, teachers), with responses ranging from 1 never/almost never to 5 almost all the time throughout the day, and a don’t know/doesn’t apply option. Respondents who answered almost all the time throughout the day on at least one item were classified as 1 intense user, and the remainder as 0 non-intense user. The items of the scale were not expected to have high intercorrelations (e.g., adolescents with intense contact with close friends were not necessarily expected to have intense contact with friends