Age changes on tests of fluid and crystallized ability for women and men on the Kaufman Adolescent and Adult Intelligence Test (KAIT) at ages 17-94 years.

Within a norm sample of 1,500 men and women, 17-94 years of age (13 age groupings), using Multivariate Analysis of Variance and Covariance, it was found that four measures designed to indicate fluid reasoning (Gf) and the composite measure of Gf declined steadily over the entire adulthood period, the decline accelerating during the period beginning at about age 55 years. Also, four measures of crystallized knowledge (Gc) and the composite measure of Gc increased through the 20s, neither increased nor decreased through mid-adulthood until about age 60 years, and declined thereafter. For the composite measures of Gf and Gc, there were no main effects or interaction effects associated with Gender. When educational attainment was covaried, small but statistically significant Gender main effects were found for four of the subtest measures of Gf and Gc; significant Gender x Age interaction effects were found for two subtests. Interpreted within Gf-Gc theory, the results replicate and extend evidence of the adulthood development of cognitive capabilities.