Most investigations in the structure of personality traits do not adequately address age; instead they presuppose a constant structure across the lifespan. Further, few studies look at the structure of personality traits a-theoretically, often neglecting to examine the relationship among indicators within a trait (coherence) and across traits (differentiation). Using a network approach, the present study examines (1) age differences in differentiation and coherence, (2) the similarity between the Big Five and network structures, and (3) the consistency of network structure across age groups in a large, cross-sectional sample. Results indicate that coherence shows early gains in adolescence with few changes across the lifespan, while differentiation mostly weakens across adulthood. The result of these age-related changes is that Big Five indicators only parallel the Big Five structure among young but not older adults. The structure of young adults tends to be quite similar while the network structures of older adults appear to greatly differ from one another. These results suggest that older adults have a different structure of personality than younger adults and suggest that future research should not assume consistency in personality structure across the lifespan.

Personality traits predict both the initiation and continued usage of alcohol and drugs. Less established is if substance use is associated with subsequent changes in personality, especially during the sensitive period of adolescence. We used three novel approaches to disentangle selection and socialization effects to address whether substance use is associated with personality development (impulsivity, sensation-seeking, depression, self-esteem). First, we used a multi-wave longitudinal sample of adolescents (N = 8,303) from the National Longitudinal Study of Youth - Child and Young Adult dataset to study the first use of a controlled substance. Second, we used propensity score weighting to equate users and abstainers on a range of background variables. Third, we investigated changes before, during, and after initiation of substances. Overall, there was unique variability and effects in personality across time for average levels, trajectories, and magnitudes of change both between users and abstainers as well as within users of specific substances. Results suggest that initiation of substance use leads to changes in personality; the specifics of which are largely contingent upon the substance being used. Impulsivity and sensation-seeking were the traits that changed the most while cocaine and cigarettes were the substances that had the largest impact.

The field of personality development almost exclusively relies on nomothetic measures (i.e., measures that are designed to capture universal, shared characteristics). Over-reliance on nomothetic measures can neglect important, individualized aspects of personality that are not captured with standard nomothetic measures. The current study takes an individual, idiographic approach to studying personality development by examining the development of one's selfconcept. Participants (N = 507) provided 20 answers to the question "who am I?" four times across a four-year period in college. These self-defining statements were categorized into seven categories (loci, activities and interests, traits, self-evaluation, goals, ideology, and student), and their change and consistency were examined in multiple ways-using rank-order consistency, mean-level change, individual differences in change, and ipsative consistency. Analyses revealed that self-concept is moderately consistent across time, but that mean-level changes occurred in six of the seven categories. Further, mean-level change in self-complexity, or the number of categories used, was also found. Mean-level changes were qualified by significant individual differences in change as well as by a wide distribution of ipsative consistency. The results suggest that young adults are both changing and maintaining the ways they describe themselves over time, some more than others. The diverse content and consistency at the individual-level demonstrates the need for more individual, idiographic assessments to thoroughly examine personality development.

Objective: Personality influences many aspects of the health process, including associations with possible mechanisms such as inflammation and health behaviors. It is currently unclear to what extent, if any, the Big Five personality traits uniquely impact later health through independent pathways of inflammatory biomarkers and health behaviors. Furthermore, it is unknown if this relationship varies for self- and informant-reports of personality. Methods: Using data from older adults (N = 1,630) enrolled in the St. Louis Personality and Aging Network study, we test whether self- and informant-reported personality (Big Five personality traits) show consistent associations with inflammation (i.e., IL-6, CRP, and TNF-α). Further, we tested whether inflammation and health behavior indirectly link personality to health outcomes through independent or shared pathways using longitudinal mediation in a structural equation modeling framework.Results: Self- and informant-reports of personality uniquely predicted future levels of inflammatory biomarkers (self bs range from -0.11 to 0.07; informant bs range from -0.15 to 0.11). Additionally, both reports of personality impacted health through biomarker and health behavior pathways. Effects were primarily found for conscientiousness (indirect effect bs range from 0.01 to 0.04) and neuroticism (indirect effect bs range from -0.01 to -0.02) and IL-6 and CRP were the biomarkers most repeatedly linked with the Big Five personality traits and health. Conclusions: Findings highlight the potential benefits of using of multiple assessments of personality and the importance of examining multiple, distinct pathways by which personality might influence later health in order to more fully understand the mechanisms underlying this relationship.

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