Maartje Boer

CHAPTER 3 60 parallel the criteria for internet gaming disorder as listed in the appendix of the DSM-5 (American Psychiatric Association, 2013; Lemmens et al., 2015). By including three additional criteria on top of the six core criteria, the SMD- scale measures problematic SMU in a way that corresponds more with the scholarly and clinical definition of behavioral addictions, thereby possibly advancing the measurement of problematic SMU. To our knowledge, validation studies on problematic SMU-scales remain limited to single-country data (Al-Menayes, 2015a; Andreassen et al., 2012; Bányai et al., 2017; Lin et al., 2017; Monacis et al., 2017; Phanasathit et al., 2015; Pontes et al., 2016; Şahin, 2018), including validation studies on the SMD- scale (Boer, Stevens, Finkenauer, Koning, et al., 2021; Savci et al., 2018; Van den Eijnden et al., 2016; Watson et al., 2020). Studies among Dutch secondary school adolescents showed that the SMD-scale had a solid unidimensional factor structure and adequate internal consistency. Also, higher values on the scale were associated with higher levels of impulsive internet use, self- declared social media addiction, and problems related to mental health, sleep, and school functioning, confirming convergent and criterion validity (Boer, Stevens, Finkenauer, Koning, et al., 2021; Van den Eijnden et al., 2016). Research among U.S. adolescents aged 13 to 19 years old showed that the scale scores provided good internal consistency and correlated strongly with scores on alternative problematic SMU scales (Watson et al., 2020). A study among Turkish adolescents aged 14 to 18 years old used an adapted version of the SMD-scale with polytomous response scales and showed adequate internal consistency and structural validity for a unidimensional scale (Savci et al., 2018). Although these single-country validation studies suggest that the SMD- scale has appropriate psychometric properties across some national contexts, these studies used different analyses and sample characteristics were diverse (e.g., with respect to age and representativeness), limiting the comparability of their findings. Adolescents’ problematic SMU can only be compared cross- nationally if it is measured with the same scale, which has been shown to be reliable and valid using identical analyses on comparable national samples. Furthermore, to secure comparability, themeasurement properties should be invariant across countries to confirmthat adolescents fromdifferent countries interpret the questions of the scale in a similar manner (Davidov, 2010; Van de Schoot et al., 2012). Cross-national research on problematic SMU is important