Means for overall Conscientiousness (A) and its facets (B), by age and gender. Single lines show the means for males, and double lines show the means for females. In Panel B, black lines show the means for Self-Discipline, and or gray lines show the means for Order. 

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... the BFI domain and facet scales were somewhat higher at older ages. Specifically, the mean reliability of the domain scales showed a positive age trend from .75 at age 10 to .83 at age 18, and was either .83 or .84 in each of the older groups. Similarly, the mean reliability of the shorter facet scales showed a positive trend from .54 at age 10 to .67 at age 18, and was between .67 and .69 in each older group. Correlations among the domain scales also differed somewhat by age. Specifically, the mean magnitude of the interscale correlations showed a negative age trend from .22 at age 10 to .16 at age 18, then a positive trend to .26 at ages 61– 65. Despite these age differences in reliability and interscale correlations, the BFI’s intended five-dimensional structure was clearly recovered in principal-components analyses conducted in each age group. In each group, a scree test indicated five meaningful dimensions, and five components were therefore extracted and varimax-rotated. Congruence coefficients were then computed to compare each component in each age group with the corresponding component in the age-21-to-25 group; this was selected as the reference group because the BFI’s intended five-dimensional structure emerged very clearly in it, as in previous studies of emerging-adult samples (e.g., Benet-Mart ́nez & John, 1998). These congruence coefficients averaged .99, and all 100 were at least .96, easily exceeding the standard of .90 that indicates factor replication (Barrett, 1986; Mulaik, 1972). Taken together, these results indicate that the overall structure of the BFI was very consistent across late childhood, adolescence, and adulthood, although there was greater measurement error at younger ages. Presentation of results. Preliminary analyses indicated that (a) almost all of the domain and facet traits assessed by the BFI showed substantial mean-level age differences, (b) some traits showed age trends that differed considerably by gender, and (c) the shapes of some trends were curvilinear and quite complex. These trends could not be closely fit by regression models, even models that included higher order polynomial age terms (quadratic, cubic, quartic, quintic, etc.) and corresponding Age ϫ Gender interaction terms. These preliminary analyses also indicated that the size of the present sample rendered conventional tests of statistical sig- nificance meaningless; for example, in the full sample, a correlation of .003 between two variables would be statistically significant at the ␣ ϭ .001 level, and a correlation of .02 would be significant at the ␣ ϭ 1 ϫ 10 Ϫ 100 level. We therefore present our results with a focus on the patterns and sizes of age and gender differences. In describing these patterns, we refer to “age trends” and “age differences”—rather than developmental “changes,” “increases,” or “decreases”— due to the present research’s cross-sectional design. For the same reason, note that we use prepositional phrases such as “across middle age,” “by late adolescence,” and “from adolescence into adulthood” to refer to cross-sectional age ranges, rather than periods of development over time. We use the T -score metric to index effect sizes; T scores are standard scores with a mean of 50 and standard deviation of 10. In terms of Cohen’s (1988) now conventional guidelines for inter- preting effect sizes, a difference of 2 T- score points represents a small effect, a difference of 5 points represents a medium effect, and a difference of 8 points represents a large effect. To control for age and gender effects when converting to T scores, we computed the overall mean of each BFI domain and facet scale by first computing its mean in each of the 112 age- and gender-specific samples (56 years of age ϫ 2 genders) and then averaging these 112 group means. Similarly, we computed the overall standard deviation of each scale as the square root of the pooled within- group variance term from a two-way (56 years of age ϫ 2 genders) analysis of variance—an estimate that controls for between-group variance. This process produced a T -score distribution uninflu- enced by the age and gender differences that are the subject of the present research. In the present sample, all pairwise age differences of at least 2 T -score points were statistically significant at the ␣ ϭ .00001 level. Mean scores on the BFI domain and facet scales, by age and gender, are shown in Figures 1–5. We calculated these group means separately for each individual combination of age and gender (age-10 males, age-10 females, age-11 males, age-11 fe- males, etc.); no smoothing functions have been applied. In each figure, single lines show the means for males, and double lines show the means for females. In Figures 1B, 2B, 3B, 4B, and 5B, black lines show the means for one facet of a domain, and gray lines show the means for the other facet. Conscientiousness. Mean levels of Order, Self-Discipline, and overall Conscientiousness are shown in Figure 1. As hypothesized, overall Conscientiousness showed very different age trends in late childhood and adolescence versus adulthood. Specifically, as shown in Figure 1A, Conscientiousness showed a negative age trend from late childhood into adolescence; the total difference was approximately 3 T -score points, or one third of a standard deviation unit. Conscientiousness then showed a pronounced positive trend from adolescence through emerging adulthood, with a total difference of approximately 7 T -score points. This trend was even more pronounced for females than for males, such that by emerging adulthood females were slightly more conscientious, on average, than were males (by approximately 2 T -score points). At the facet level, Figure 1B illustrates that Self-Discipline and Order showed age trends across these years similar to overall Conscientiousness, with negative trends from late childhood into adolescence (with total differences of 2 or 3 T -score points), then pronounced positive trends through emerging adulthood (with total differences of 5 or 6 T -score points). Gender differences in these two facets, however, related differently with age. Like overall Conscientiousness, a small gender difference in Self-Discipline was first present in emerging adulthood. In contrast, females were more orderly than males, on average, at each age from 10 to 65. Overall Conscientiousness showed a further, although less pronounced, positive trend across early adulthood and middle age, with age differences of approximately 5 more T -score points for both males and females. At the facet level, as hypothesized, these differences were substantial for Self-Discipline (approximately 6 T -score points), but only trivial for Order (approximately 1 T -score point). Altogether, the total age differences from adolescence through middle age were approximately 11 T -score points for overall Conscientiousness and Self-Discipline. These are very large cross-sectional age effects that equal the difference between scores at the 50th and 86th percentiles of a normal distribution. The total age difference for Order was approximately 7 T -score points, a substantial effect that equals the difference between scores at the 50th and 76th percentiles of a normal distribution. Agreeableness. Mean levels of Altruism, Compliance, and overall Agreeableness are shown in Figure 2. As hypothesized, overall Agreeableness showed age trends similar to Conscientiousness, although the trends for Agreeableness were somewhat less pronounced. As shown in Figure 2A, Agreeableness showed a negative trend from late childhood into adolescence (with a total difference of approximately 2 T -score points), a positive trend from adolescence into emerging adulthood (with a total difference of approximately 3 T -score points), and a further positive trend across early adulthood and middle age (with a difference of approximately 3 more T -score points). The total difference of 6 T -score points from adolescence through middle age represents a substantial age effect, equal to the difference between scores at the 50th and 73rd percentiles of a normal distribution. At the facet level, Figure 2B illustrates that Altruism and Compliance showed age trends similar to overall Agreeableness, with only one qualification: Compliance did not show a negative trend from late childhood into adolescence for males. Instead, males showed low levels of Compliance even at age 10, a finding unlikely to surprise elementary-school teachers. Regarding gender differences more generally, at each age females were somewhat more agreeable, altruistic, and compliant, on average, than were males (by approximately 2 T -score points). Neuroticism. Mean levels of Anxiety, Depression, and overall Neuroticism are shown in Figure 3. There were only trivial gender differences in these traits at age 10 (less than 1 T -score point), but, as hypothesized, there were very different age trends for males versus females across late childhood, adolescence, and adulthood. For females, Anxiety and overall Neuroticism showed positive trends into adolescence (with total differences of approximately 3 T -score points), flat trends through emerging adulthood, and then negative trends across early adulthood and middle age (with total differences of approximately 5 T -score points). In contrast, males’ mean levels of Anxiety and overall Neuroticism showed slightly negative trends from late childhood through middle age (with total differences of approximately 2 T -score points). Substantial gender differences in both of these traits (of approximately 5 T -score points) were present by midadolescence, such that females were more prone to anxiety and other negative emotions, on average, than were males. The magnitudes of these gender differences diminished across early adulthood and middle age, although a small difference (of approximately 2 T -score points) was present even at the end of middle age. Age trends ...