IQ at Age 11 and Longevity: Results from a Follow-Up of the Scottish Mental Survey 1932

Abstract

Childhood social factors - such as education, occupational status and relative social deprivation - are known to affect longevity. Mental ability differences in childhood are related to these social factors. However, there are few studies of the association between mental ability in childhood and survival. Here we examine the association between IQ at age 11 and survival to age 76 in a follow-up study of the Scottish Mental Survey of 1932 (SMS 1932). In the SMS 1932 all children born in 1921 and attending school in Scotland on June 1, 1932 were given the same valid mental ability test (an IQ-type test) under the same conditions. We chose the 2792 children from schools in the Aberdeen area of Scotland as our target population. We searched public and health records in Scotland, England and Wales to discover whether they had died or were still alive on January 1, 1997. Copies of death certificates were obtained. Deaths certified as due to cancer were noted. The association between childhood IQ and survival was studied using Cox proportional hazards regression (Whalley and Deary 2001). People with higher childhood IQ scores tended to live longer. The association differed between the sexes. The association in women was maintained across the life span. In men, the association was reversed during World War II: those with a higher IQ had a higher risk of dying during that period. Controlling for overcrowding in the person’s school area did not account for the association between IQ and survival. In the present report we examine for the first time the odds ratios of survival for IQ groups (divided into quartiles) for men and women. We find evidence of a deleterious effect of low IQ and a protective effect of belonging to the highest IQ group. The association between childhood IQ and risk of death from cancer is examined. Dying from cancer, and more specifically stomach and lung cancers, is associated with lower childhood IQ scores.