Age-related IQ decline is reduced markedly after adjustment for the Flynn effect

Abstract

Twenty-year-olds outperform 70-year-olds by as much as 2.3 standard deviations (35 IQ points) on subtests of the Wechsler Adult Intelligence Scale (WAIS). We show that most of the difference can be attributed to an intergenerational rise in IQ known as the Flynn effect. Normative data from different versions of the WAIS enabled us to estimate the degree to which the Flynn effect, rather than age-related decline, contributes to differences between 20- and 70-year-olds. The Flynn effect accounted for 38–67% of the apparent age-related decline on 6 of the 11 subtests. On the other 5 subtests, all of which are categorized as verbal, the Flynn effect was larger than the age-group difference. For these verbal subtests, the Flynn effect masked a modest increase in ability as individuals grow older. Overall, the Flynn effect accounted for at least 85% of the disparity between 20‐ and 70-year-olds.

Keywords:

• Aging
• Flynn effect
• Cohort effect
• Gerontology
• Intelligence
• IQ testing

The authors thank James R. Flynn for providing prepublication drafts of articles and other information that facilitated the writing of this paper. We appreciate the suggestions received from Arturo Hernandez and other members of the developmental cognitive neuroscience faculty of the Department of Psychology, University of Houston.