Maartje Boer

CROSS-NATIONAL VALIDATION OF THE SMD-SCALE 67 3 Results Sample Characteristics The initial sample includes 47 countries ( n = 244,097). Three countries were excluded because they did not survey problematic SMU ( n = 10,576). Adolescents who responded ‘ not applicable/don’t know ’ to all items of the intensity of online communication scale automatically skipped the questions on problematic SMU and were also excluded from the sample (ranging from 1.78% in North Macedonia to 17.62% in Azerbaijan, n = 10,989). This yielded a sample of 222,532 adolescents from 44 countries (listed in the tables from the Appendix). From these countries, the average school and participant response rates were 69.70% and 80.34%, respectively (Inchley et al., 2020a). Adolescents were on average 13.54 years old ( SD = 1.63, min. = 10.00, max. = 16.50) and 51.24% were girls. Cronbach’s alpha for psychosomatic complaints was 0.81, which indicates good reliability (Gadermann et al., 2012). Cronbach’s alpha was not calculated for the other study measures, because they either consisted of one item (life satisfaction) or were considered as a formative scale (intensity of online communication, socioeconomic status), which means that not all items were expected to have high intercorrelations (Bollen & Lennox, 1991). Missing data on the study measures ranged between 0.65% (age) and 10.14% (problematic SMU: escape). Little’s Chi-square test for missing data showed that these data were not completely missing at random (Chi- square(55,103) = 82,498.58, p < 0.001), which implies that imputation of missing data is required in order to prevent potential bias (Enders & Bandalos, 2001). Prevalence Differences Table 3.1 shows that the most prevalent symptoms were ‘persistence’ (30.66%) and ‘escape’ (30.74%). The least prevalent symptoms were ‘conflict’ (14.38%) and ‘deception’ (14.56%). Figure 3.1 shows that over a third of adolescents did not report symptoms, whereas 7.64% reported problematic SMU, that is, six or more symptoms. By country, problematic SMU ranged between 3.20% (Netherlands) and 16.41% (Malta). All prevalence rates of problematic SMU (symptoms) by country can be found in the Appendix (Table A3.2).