Intelligence and education as predictors of cognitive state in late life: a 50-year follow-up

We evaluated the relation of education and intelligence in early adult life to cognitive function in a group of elderly male twins. The Army General Classification Test (AGCT) was administered to US armed forces inductees in the early 1940s. Fifty years later, as part of a study of dementia in twins, we tested the cognitive status of 930 of these men using the modified Telephone Interview for Cognitive Status (TICS-m). TICS-m scores obtained in later life were correlated with AGCT scores (r = 0.457) and with years of education (r = 0.408). Thus, in univariate analyses, the AGCT score accounted for 20.6% and education accounted for 16.7% of variance in cognitive status. However, these two effects were not fully independent. A multivariable model using AGCT score, education, and the interaction of the two variables as predictors of the TICS-m score explained 24.8% of the variance, a slightly but significantly greater proportion than was explained by either factor alone. In a separate analysis based on 604 pairs of twins who took the AGCT, heritability of intelligence (estimated by AGCT score) was 0.503. Although this study does not address the issue of education and premorbid IQ as risk factors for dementia, the findings suggest that basic cognitive abilities in late life are related to cognitive performance measures from early adult life (ie, education and IQ).