Within-Person Fluctuations in Objective Smartphone Use and Emotional Processes During Adolescence: An Intensive Longitudinal Study

Since the advent of smartphones, peer interactions over digital platforms have become a primary mode of socializing among adolescents. Despite the rapid rise in digital social activity, it remains unclear how this dramatic shift has impacted adolescent social and emotional experiences. In an intensive, longitudinal design (N = 26, n = 206 monthly observations for up to 12 months, 12-17 years), we used digital phenotyping methods to objectively measure within-person fluctuations in smartphone use (screen time, pickups, notifications) across different categories (social media, communication, entertainment, games) and examined their prospective, bidirectional associations with positive and negative mood. Bayesian hierarchical models showed that when adolescents reported better mood than usual, they subsequently spent more time on communication apps and launched social media and communication apps upon pickup less often. Meanwhile, when adolescents used entertainment apps more than usual, they subsequently reported improved mood. These preliminary findings suggest a pattern where fluctuations in mood relate to subsequent changes in smartphone use that are primarily social, whereas the fluctuations in smartphone use relating to subsequent changes in mood were primarily entertainment-related. We found little evidence that within-person fluctuations in screen time or social media use were associated with increases in negative mood, as frequently theorized. These findings highlight the importance of disentangling the distinct components of smartphone use that relate to affective processes and examining their bidirectional, prospective relationships over time, due to the possibility of differential outcomes. This work is a necessary first step in identifying targets for intervention efforts promoting resilience and wellbeing during adolescence.