Combining Life History Calendars and Ecological Momentary Assessment for Evaluating Everyday Stress and Its Impact on Mental Health in Healthy Adults: Longitudinal Study.

Stress is a well-established risk factor for a range of negative health outcomes, making the longitudinal assessment of everyday stress increasingly important. This study tested the feasibility of combining a prospective assessment of stress responses using Ecological Momentary Assessment (EMA) with a retrospective evaluation of stressors via a Life History Calendar (LHC). It also examined how different operationalizations of stress components-reactivity, recovery, and pileup-using various intra-individual baselines influenced stressor count, mental health symptoms, and trait anxiety. A sample of 165 adults (50.9% female; M age = 24.91 years, SD = 4.61) was followed over six months. Stress responses were assessed prospectively via EMA, administered three times daily, and stressor exposure was retrospectively captured using the LHC. We computed indices of stress reactivity, recovery, and pileup using three baseline types: local (1-week and 2-week periods prior to a stressor episode) and a cumulative average of all prior stressor-free weeks. Hierarchical multiple regression analyses examined associations between these indices and changes in mental health symptoms and trait anxiety. Combining EMA and LHC methods to assess stress components was feasible. Baseline choice influenced both stressor episode counts and the associations between stress components and mental health outcomes. Stress reactivity and pileup, based on both local and cumulative baselines, were consistently associated with increases in mental health symptoms. Only one operationalisation of stress recovery was linked to changes in symptoms. Trait anxiety was not associated with any stress component, except for pileup when using a 1-week local baseline. These findings support the feasibility of integrating EMA and LHC methods to assess stress dynamics. Different baseline definitions yield distinct results, highlighting the importance of carefully selecting baseline parameters in stress research. This has important implications for designing and refining future studies on stress and health.