Abstract
BACKGROUND: As a critical period in psychosocial development, adolescence is marked by heightened emotion regulation demands as well as increased risk for, and vulnerability to, stress. OBJECTIVE: This longitudinal study investigates how dynamic patterns (ie, mean intensity, variability, instability, inertia, and reactivity to stress) in positive and negative affect relate to, and predict change in, broad domains of adolescent psychosocial well-being (ie, mental health, social well-being, and academic motivation). Using a daily diary procedure to capture adolescents' daily naturalistic affective experiences, this study will provide novel insights into how affective processes predict psychosocial well-being over time beyond traditional, static assessment. METHODS: At baseline, adolescents aged 14-17 years from Southwestern Ontario reported on their academic motivation (eg, extrinsic motivation), social well-being (eg, social support and loneliness), and mental health (eg, anxiety syndrome severity) before completing a 35-day smartphone-based daily diary protocol wherein participants reported twice daily in the morning (ie, 7-10 AM) and evening (ie, 8-11 PM) on positive and negative affect, stress, and internalizing symptom severity. Participants then repeat the surveys of academic motivation, social well-being, and mental health 6, 12, and 18 months following baseline assessment to assess change in each domain of psychosocial well-being over time. RESULTS: Adolescents (N=149) were enrolled into this longitudinal study between April 2023 and November 2024, such that all participants will complete the scheduled 18 months of longitudinal follow-up assessments by May 2026. Primary study analyses will use multilevel modeling, structural equation modeling, multilevel structural equation modeling, and dynamic structural equation modeling to examine how dynamic patterns in positive and negative affect (eg, instability, inertia) concurrently correlate with, and prospectively predict change in, psychopathology and well-being. CONCLUSIONS: This study protocol paper outlines the overarching study objectives and methodology to promote transparency and reproducibility. Through the integration of daily diary methodology within a longitudinal design, this study aims to clarify the potential implications of dynamic affective processing (eg, affective reactivity to daily stress) for both adolescent psychopathology and well-being beyond clinical syndromes. INTERNATIONAL REGISTERED REPORT IDENTIFIER (IRRID): DERR1-10.2196/76333.