Maartje Boer

CHAPTER 8 232 Abstract The present study examined five possible explanations for the mixed findings on the association between adolescents’ social media use (SMU) intensity and wellbeing. Particularly, it investigated whether the association between SMU intensity and life satisfaction depended on (1) the type of SMU activity the adolescent engaged in, (2) the (non)linearity of the association, (3) individual differences, (4) inclusion of SMU problems, and (5) the level of analysis. Data from four waves of longitudinal data among 1,419 adolescents were used ( M age(T1) = 12.51 (0.60), 45.95% girl). Multilevel analyses showed that at the within-person level, on average, changes in different types of SMU activities were not associated with changes in life satisfaction. Within individuals, the associations ranged from negative to positive across adolescents. In general, this variation could not be explained by adolescents’ engagement in upward social comparisons. At the between-person level, the higher adolescents’ average intensity of certain SMU activities, the lower their average level of life satisfaction. However, these associations were confounded by adolescents’ SMU problems. No curvilinear associations were found. Overall, the findings underline that to enhance our understanding of the association between SMU and wellbeing in adolescence, it is important to acknowledge the heterogeneity of effects, distinguish between SMU intensity and SMU problems, and disentangle within- from between-person effects. Keywords : Social media use, wellbeing, life satisfaction, adolescents, longitudinal study.