Variance profiles of affective and cognitive processes in daily life: Differences between people, across days, and within days.

Ecological Momentary Assessments (EMA) of psychological constructs enables examination of between-person differences and within-person fluctuations across timescales: across days and within days. Research has mostly focused on between/within-person levels and on affect dynamics, leaving potential within-person timescale distinctions and self-reported cognitive processes understudied. We applied multilevel variance decomposition to EMA items from the HowNutsAreTheDutch study (30 days; three daily beeps/assessments; N = 1299; t = 60,189; 84% female; mean age = 39; range = 16-86), partitioning their variance into: between-person, within-person/across days, within-person/within-day (structured by the beeps), and residual/unexplained within-person/within-day variance. We analysed positive affect (PA), negative affect (NA), and self-reported cognitive processes across three domains: evaluative, perseverative, and concentration. Cognitive items showed higher average between-person variance than NA and PA (61.8%, 53.1%, 34.5%, respectively). Within-person/across days variance was moderate (7%-15.9%), while structured within-person/within-day variance was minimal (0.3%-2.8%). Residual variance was largest for PA, then NA, and smallest for cognition (averages of 47%, 33.4%, 26.9%, respectively). Total within-person variance (across days, within day, and residual) was comparable to between-person variance for most items, and exceeded it for PA, suggesting that psychological variables contain both state and trait components to varying degrees. Overall, results revealed heterogeneous variance profiles, which are dependent on construct type, level of observation, and timescale.