UC Davis

Religion is not as popular or widespread in the world as it was decades ago. Despite this ongoing worldwide secularization trend, individual differences in religiosity are still prevalent and associated with a variety of psychological variables. In particular, individual differences in religiosity both predict and are predicted by individual differences in personality. Given the influence religion has on identity, politics, and society, it is important to understand changes over time in religiosity amidst secular declines and how these changes impact personality. This dissertation consists of two chapters. In Chapter 1, I analyzed religiosity development across the lifespan while controlling for ongoing secularization trends using longitudinal data from over 14,000 Dutch participants aged 16 to 101 years. Results from a series of mixed growth curve models indicated that religiosity increases across the lifespan, with no evidence for age-graded decreases in religiosity after controlling for secularization. Increases were most pronounced during middle to late adulthood and moderated by education, such that college-educated individuals were less religious and experienced less pronounced age-graded increases in their religious beliefs. In Chapter 2, I investigated between- and within-person associations between religiosity and the Big Five personality traits in a sample of over 12,000 Dutch individuals across 11 years. Results from random intercept cross-lagged panel models (RI-CLPM) at the between-person level indicated religiosity was associated with higher levels of agreeableness and conscientiousness, and lower levels of emotional stability, extraversion, and openness. At the within-person level, when people experienced an increase in agreeableness and/or extraversion relative to their usual levels, they tended to subsequently believe more strongly in God than usual, and this effect was bidirectional for agreeableness. Between-person associations were moderated by gender and religious upbringing. Religiosity was negatively associated with extraversion for women and positively associated with agreeableness and conscientiousness for men; people who grew up in a religious family had a stronger negative association between religiosity and openness. Taken together, results from both studies show that religion is still pervasive and influential on personality despite worldwide declines in religiosity.