Usually, I don’t ruminate, only from time to time: disentangling the associations between trait and state measures of rumination and affect at multiple timescales

Recent experience sampling research on affective functioning has emphasised the importance of short-term dynamics, yet rarely evaluates whether momentary measures are better explained by stable individual differences or by within-individual fluctuations. To address this issue, we (1) decomposed the variance in momentary affect explained by rumination across the between- and within-person levels, and (2) compared the predictive validity of state-based (<i>mean state</i>) and global (<i>trait</i>) self-report rumination measures of between-person differences. Our sample comprised 247 individuals who received eight questionnaires every day for up to 28 days, assessing their momentary affective states and emotion regulation, yielding 14,265 observations. Our results showed that rumination indices explained 2-3 times more variance in momentary negative affect at the between-individual level than at the within-individual level. Mean state rumination and global self-reports were only moderately correlated, and the former explained roughly twice as much variance of negative affect. For positive affect, both predictors conveyed similar, weak predictive validity. These findings suggest that longer-term tendencies in emotion regulation are more relevant predictors of affect than momentary fluctuations. We propose that aggregated momentary measures may capture individual differences with greater validity than global self-reports, emphasising the importance of accounting for timescale in experience sampling research.