Adolescents’ Daily Affect Predicts Their Mobile Phone Use (Not the Other Way Around)

Concerns about adolescent screen time have fueled debates about the role of mobile phone use in adolescent development, yet most research has relied on cross-sectional self-reports and global measures of use. The present study advances the field by using objective, naturalistic data to differentiate active from passive phone use and test within-person associations with adolescents’ morning affect and sleep. We applied multilevel models to 3,192 daily observations from 40 adolescents (ages 15–20; 65% male) collected over a 90-day period using the Effortless Assessment Research System. Results showed that higher-than-usual morning negative affect predicted greater passive use the same day, whereas morning positive affect did not predict active or passive use. In contrast, neither the amount of active nor amount of passive use predicted subsequent sleep outcomes or next-day affect. These findings suggest that adolescents’ morning negative affect may shape how they engage with their phones, while fears about downstream effects of phone use on sleep and affects may be overstated.