Adolescence is a pivotal developmental window for the emergence of internalizing disorders, particularly depression and anxiety. Numerous biological, psychological, and environmental factors contribute to this vulnerability, including sleep disturbances that often co-occur with internalizing symptoms. Nonetheless, individual differences in daily sleep–mood dynamics remain largely unexplored. This thesis addresses this gap by examining specific links between sleep–mood dynamics and internalizing symptoms through Ecological Momentary Assessment (EMA).
First, an updated meta-analysis quantifies missing data in youth EMA research and identifies key design- and sample-related moderators of acceptance, compliance, and retention. The findings underscore substantial heterogeneity across studies, highlighting the need for transparent reporting. Second, the mSanté study protocol outlines a multi-wave ambulatory assessment design that intensively tracks adolescents’ daily lives over several weeks through concurrent actigraphy, EMA, and periodic questionnaires. This methodological framework captures evolving patterns of sleep and daytime experiences in both clinical and non-clinical youth contexts. Third, analyses of mSanté data reveal meaningful individual differences in the within-person coupling (WPC) of sleep patterns and subsequent daytime mood, which correlate with anxiety symptom severity. These findings suggest that daily sleep–mood fluctuations may serve as early markers of risk or resilience, informative for preventive intervention.
Overall, this thesis situates the results within a broader scientific perspective, integrating methodological advances in EMA with new insights into adolescent sleep–mood interplay. By adopting an idiographic lens on sleep–mood dynamics, the project identifies temporal markers linking sleep disturbances with emerging internalizing disorders. In doing so, it advocates for a dynamic research agenda that refines EMA methodologies and leverages longitudinal assessments to enhance both scientific understanding and clinical practice in adolescent mental health.