Maartje Boer

CHAPTER 9 286 Summary and Discussion The aim of the present dissertation was to enhance current knowledge on the association between social media use (SMU) and adolescent wellbeing. More specifically, we focused on the differences between SMU problems and SMU intensity, in particular in their differential associations with wellbeing. Throughout the dissertation, wellbeing most often refers to mental health, assessed by indicators of positive mental health (i.e., life satisfaction, self- esteem), as well as mental health problems (i.e., depressive symptoms, symptoms of attention deficit hyperactivity disorder (ADHD), psychosomatic complaints, and emotional, peer, and conduct problems). In addition, we also studied other domains related to adolescent wellbeing, namely social wellbeing (i.e., friends and family support, face-to-face contact with friends, perceived friendship competence), school wellbeing (i.e., school satisfaction, perceived schoolwork pressure), and sleep (i.e., sleep duration and sleep quality). In this final chapter, we first summarize the main findings by chapter. Subsequently, we integrate the findings from the chapters intro six key findings. After that, we discuss the implications of our findings, divided into conceptual, methodological, theoretical, and practical implications. Then, we discuss four future research directions that emerged from our studies and we outline the strength and limitations from our studies. Finally, we end this chapter with a conclusion. Summary of the Main Findings by Chapter There is little large-scale validation research on instruments measuring problematic SMU. Chapter 2 investigated the psychometric properties of the nine-itemSocialMediaDisorder (SMD)-scalewithinanationally representative cross-sectional sample of 6,626 Dutch adolescents. Findings showed that the scale had a solid unidimensional factor structure, confirming structural validity. Also, the items showed high internal consistency, suggesting good reliability. The scale showed to bemost informative at moderate to high scores on the scale’s continuum, which implies that the scale measures moderate to high levels of SMU problems most reliably. In addition, the factor structure was measurement invariant across gender, age, ethnic backgrounds, and