Personality development from early to middle adulthood in the general population and those with mental health difficulties.

We describe personality trait maturation from early to middle adulthood in the population and in populations with common mental health or substance use problems to inform personality-sensitive public health and health services care. Data were drawn from the population-based Victorian Adolescent Health Cohort Study. Traits were measured using the NEO Five Factor Inventory at 24 and 42 years. We estimated trait rank-order stability, mean-level change, and standardised mean difference (SMD) scores in subgroups defined by patterns of substance use and common mental disorder from adolescence (15-17 years) to adulthood (21-35 years). Multiple imputation was used to address missing data for the full sample of 1,943 participants. Between early and middle adulthood, population-levels of agreeableness and conscientiousness increased; extraversion, neuroticism, and openness decreased. These patterns were also largely present in those within subgroups, the most pronounced drop being neuroticism in those with persistent common mental disorder (SMD - 0.31, 95% CI -0.41 to -0.18). Compared with other subgroups and the overall population averages, for this group with persistent mental disorder, neuroticism was higher on entry to adulthood, dropped more substantially over time, but still remained high in middle adulthood. A similar decline was not observed for those with no or transient mental disorder, who entered adulthood with lower neuroticism. Subgroup results for neuroticism imply some variation in the timing of maturation by the presence and duration of common mental disorder. Those who present clinically with long-term anxiety and/or depression may require additional support for midlife personality difficulties that may negatively impact adult roles and functioning.