Age and WAIS-R intelligence in a national sample of adults in the 20- to 74-year age range: A cross-sectional analysis with educational level controlled

Abstract Age differences in intellect as reflected in WAIS-R performance from age 20 to 74 years were evaluated while educational attainment levels were held constant. The seven adult age groups (ranging from 20–24 to 70–74) in the WAIS-R standardization sample, comprising a sample of 1480 men and women, provided the data source. The data were analyzed using regression analysis and a weighted means approach. The 25–34-year age group served as the target sample for this study; the mean scores for adults in each educational category, within each age group, were weighted to match the educational distribution of ages 25–34. After weighting for education, the decline in mean Verbal IQ from age to age disappeared. However, declines across the 20–74-year range remained for Performance IQ and Full Scale IQ, even after controlling for education. The relationship between education and each of the 11 subtests was also evaluated; the resuls were interpreted as supportive of Horn's fluid-crystallized explanation of changes in intelligence with advancing age.