Nguyen, Le Phuong Linh2024-07-242024-07-242024-05https://hdl.handle.net/11299/264339University of Minnesota Ph.D. dissertation. May 2024. Major: Psychology. Advisor: Moin Syed. 1 computer file (PDF); x, 263 pages.Personality research has established robust associations between traits and a variety of life outcomes. Nevertheless, much of the literature relies on the Big Five traits, which broadly encapsulate important patterns of psychological individual differences. As a result, this broad conceptualization often leads to weaker associations with outcomes within specific domains. The current dissertation offers a comprehensive examination of different ways to expand upon traditional trait research. This includes combining multiple levels of personality constructs both within and outside of the Big Five framework, multiple perspectives through self and informant reports, and multiple timescales from one-time trait measures to dynamic state fluctuations and longitudinal trait changes. The primary focus is on intraindividual variability, or how people change in their psychological processes across time, and its relevance within the highly influential life domain of romantic relationships. Study 1 presents a preregistered meta-analytic review across k = 88 independent samples (N = 20,813) of the association between personality traits at both the domain (Big Five) and metatrait (Stability and Plasticity) levels with affective variability. We found a positive association between affective variability and Plasticity as well as its underlying traits. However, the pattern of findings was mixed and valence-specific for the Stability traits, and this metatrait itself was negatively associated with variability in Positive Affect but positively so for variability in Negative Affect. Study 2 further investigated intraindividual variability in psychological processes by examining assortative mating patterns in 138 established romantic couples using experience sampling methods of personality and affective states across 35 time points during a 7-day period. We found evidence for assortative mating based on both baseline traits and dynamic states. However, there was more evidence for perceived similarities than actual similarities at baseline, and there was much more evidence for dynamic similarities on states than baseline similarities on traits. There was also evidence for a complementarity effect or negative between-partner correlation on Volatility. Study 3 expanded the timescale from dynamic short-term state fluctuations to longitudinal trajectories of trait change across multiple months and years, examining assortative mating patterns in two complementary samples of early dating couples (N = 184) and married or cohabiting couples (N = 168). We found evidence for assortative mating across various relationship-specific characteristics both at baseline and longitudinally, which were often stronger in magnitude than assortment on Big Five traits. Consistent with Study 2, couples often perceived each other to be more similar than their actual similarity indicated. Nonetheless, in line with the literature, there was little evidence to support the benefits of between-partner similarity for relationship quality, especially after controlling for actor and partner effects of both partners’ individual characteristics. Altogether, this research program provides a broad and thorough examination of intraindividual variability in general as well as in the interpersonal context, and in doing so contributes to both the substantive body of literature and the methodological considerations needed when investigating these personality processes.endyadic studyintraindividual variabilitylongitudinal studymeta-analysispersonality psychologyromantic relationshipsThesis or Dissertation