Are state–trait fit and state–situation fit relevant for within-person dynamics of personality states?

Fit hypotheses are a common theme in psychological theories. Various theoretical approaches postulate that fit is also relevant for the within-person dynamics of personality states. A better understanding of these dynamics is important to comprehend the functioning of personality and its relations to relevant life outcomes. Two forms of fit are relevant for personality states: personality states that fit with characteristics of the current situation (state-situation fit) and personality states that fit with personality trait levels (state-trait fit). Both forms of fit are assumed to be related to more positive affect. In three intensive longitudinal studies (Sample 1: N = 194, 4,244 observations; Sample 2: N = 254, 7,667 observations; Sample 3: N = 374, 16,418 observations), we conducted moderated multilevel polynomial regression and response surface analysis to examine whether trait-state fit and state-situation fit were associated with state affect. Generally, there was no consistent evidence for state-trait fit, state-situation fit, or interactions between personality traits, personality states, and situation characteristics predicting momentary state affect. The analyses yielded several spurious significant fit and interaction effects that could however not be replicated in the other samples. Taken together, in one of the most comprehensive attempts to demonstrate fit effects in personality states to date, we could not find any consistent evidence for fit or interactions between personality traits, personality states, and situation characteristics predicting momentary affect. Furthermore, these findings emphasize the importance of replications and robustness checks when examining complex personality dynamics such as fit or interactions. (PsycInfo Database Record (c) 2024 APA, all rights reserved).