From Who experiences stress to When It Occurs: Revisiting Lazarus' transactional model of stress using an ecological momentary assessment framework.

According to the Transactional Model of Stress, stress responses arise from one's perceptions of situational relevance (primary appraisal) and coping resources (secondary appraisal) as being insufficient. Although the model assumes moment-to-moment within-person variability, most research evidence stems from cross-sectional study designs. Therefore, this study applies Ecological Momentary Assessment (EMA) to test the dynamic interplay between primary and secondary appraisals and fluctuations in perceived stress. We used EMA data from the TrackYourStress platform to examine both interindividual ("who") and intraindividual ("when") associations between primary and secondary appraisals and perceived stress. Bayesian multilevel models were applied to 2,908 observations from 164 participants. These models showed that higher appraisal of situational relevance was associated with increased stress, whereas higher appraisal of coping resources was associated with lower stress levels. Importantly, the association between relevance appraisals and stress was stronger under low coping resource appraisals. Findings were present at the inter- and intraindividual level. These findings support the model's dynamic assumptions and highlight that appraisals not only account for interindividual differences in stress levels but also for moment-to-moment variation in stress responses in daily life.