Adolescents' daily affect predicts their mobile phone use (not the other way around).

Higher-than-usual morning negative affect predicted greater passive mobile phone use on the same day.

• The association was within-person, meaning it reflected deviations from each adolescent's own typical level of negative affect.
• Passive phone use was defined as foreground app time without keyboard input.
• No corresponding association was found between morning positive affect and passive phone use.
• This directional finding suggests affect shapes phone use, not the reverse.

Morning positive affect was not associated with either active or passive mobile phone use on the same day.

• Both active use (time with keyboard input) and passive use were examined as outcomes.
• The null finding for positive affect held within the same multilevel modeling framework used for negative affect.
• This suggests the affect-phone use relationship may be specific to negative emotional states.

Daily fluctuations in active and passive mobile phone use did not predict sleep that night.

• Neither active use (keyboard input time) nor passive use (remaining foreground app time) on a given day predicted sleep outcomes.
• Sleep was assessed the night following the phone use measurement.
• Data were collected over a 90-day period using the Effortless Assessment Research System (EARS) on Android devices.
• The sample consisted of 40 adolescents ages 15–20, yielding 3,192 daily observations.

Daily fluctuations in active and passive mobile phone use did not predict next-morning affect.

• Neither active nor passive phone use on a given day predicted morning affect (positive or negative) the following morning.
• This directional test was conducted within multilevel models applied to 3,192 daily observations.
• The finding challenges a commonly assumed directionality in which phone use harms emotional well-being.

The study used objective, naturalistic measures to distinguish active from passive mobile phone use over a 90-day period.

• Active use was defined as time with keyboard input; passive use was defined as remaining foreground app time without keyboard input.
• Data were collected using the Effortless Assessment Research System (EARS) on Android phones.
• The sample included 40 Android-using adolescents (ages 15–20; 65% male), yielding 3,192 daily observations.
• The 90-day naturalistic data collection period allowed within-person analysis of daily associations.
• The authors noted reliance on often cross-sectional and self-reported global measures as a limitation in prior research that this study addressed.