Maartje Boer

Table of Contents Chapter 1 Introduction 7 Chapter 2 Validation of the Social Media Disorder-Scale in adolescents: Findings from a large-scale nationally representative sample 25 Chapter 3 Cross-national validation of the Social Media Disorder- Scale: Findings from adolescents from 44 countries 57 Chapter 4 Adolescents' intense and problematic social media use and their well-being in 29 countries 101 Chapter 5 Attention deficit hyperactivity disorder-symptoms, social media use intensity, and social media use problems in adolescents: Investigating directionality 127 Chapter 6 Social media use intensity, social media use problems, and mental health among adolescents: Investigating directionality and mediating processes 153 Chapter 7 The course of problematic social media use in young adolescents: A latent class growth analysis 191 Chapter 8 The complex association between social media use intensity and adolescent wellbeing: A longitudinal investigationof five factors thatmayaffect theassociation 231 Chapter 9 Summary and discussion 285 Samenvatting [Summary in Dutch] 317 References 333 Dankwoord [Acknowledgements] 361 Curriculum Vitae 3 69