Maartje Boer

SUMMARY AND DISCUSSION 295 9 (suggested) behavioral addictions, such as internet gaming disorder and gambling disorder (American Psychiatric Association, 2013). Thus, the nine- item SMD-scale is a more comprehensive conceptualization of problematic SMU, that is more in line with the scholarly and clinical definition of behavioral addictions. The finding that higher levels of SMU problems were persistent (Key finding 5; Chapters 6-8), together with the finding that SMU problems were negatively related to multiple domains of wellbeing (Key finding 2; Chapters 4-6, 8), is important for thediscussiononwhether problematic SMU represents addictive behavior, as the SMD-scale intends. Although problematic SMU is measured with symptoms of addiction similar to substance addiction criteria, it has been argued that, despite such an operationalization, problematic SMU may not represent addiction (Kardefelt-Winther et al., 2017; Van Rooij & Prause, 2014). Several scholars stressed that two main criteria define behavioral addiction: First, the behavior in question leads to significant harm or distress and second, the behavior is persistent or recurs for a significant period of time (Billieux, King, et al., 2017; Billieux, Van Rooij, et al., 2017; Kardefelt-Winther et al., 2017). These criteria are also included in the criteria for recognized behavioral addictions, including gambling and gaming disorder, in the latest version of the International Classification of Diseases (ICD-11; World Health Organization, 2019). Scholars are concerned that those reporting addiction symptoms like substance addiction symptoms related to normative everyday activities, such as SMU, do not meet the aforementioned two key criteria of behavioral addiction. For example, preoccupation with social media may not interfere with daily life in the same way that preoccupation with substances does. Therefore, scholars emphasized that the application of substance use criteria to identify behavioral addictions may not be justified (Kardefelt- Winther et al., 2017). However, our findings challenge this criticism, because both our studies showed that adolescents with higher levels of SMUproblems, as defined by substance addiction criteria, reported impaired wellbeing in several life domains (Chapters 4-6, 8). Furthermore, they continued to show high levels for a prolonged period of time (Chapter 7). Thereby, these findings support the idea that problematic SMU, as defined by substance addiction criteria, reflects addiction-like behavior. Nevertheless, more research is essential to verify the suggestion that