WAIS-III IQs, Horn's theory, and generational changes from young adulthood to old age

Abstract

This paper examined age changes in intellectual ability across the broad 16- to 89-year age range. The results of two studies, both involving IQs on the recently published WAIS-III, are presented and integrated to address issues concerning the relationship of IQ to age, most notably how this relationship (a) provides greater insight into Horn's expansion and elaboration of fluid-crystallized theory and (b) has changed from one generation to the next when the data are analyzed in the context of data on the WAIS, WAIS-R, and other intelligence tests for adults. Study 1 was a cross-sectional investigation based on standardization data from the WAIS-III manual and data provided by the test publisher that evaluated changes on the three WAIS-III IQs, controlling for the important cohort variable of educational attainment. Study 2 was a longitudinal investigation with independent samples that examined the Verbal, Performance, and Full Scale IQs of seven cohorts at three points in time over a span of 17 years. For the latter study, the data source was normative data from the WAIS-R and WAIS-III, with appropriate adjustments for errors due to changes in instrumentation and time lag. Results were interpreted in the context of Horn's theory, especially his distinction between maintained and vulnerable abilities. Differences in age patterns from the 1950s through 1970s versus the 1980s and 1990s were interpreted from the perspective of real generational changes in the age–IQ relationship.