Childhood mental ability and lifetime psychiatric contact: A 66-year follow-up study of the 1932 Scottish Mental Ability Survey

We test the hypothesis that intelligence is related to the risk of mental illness by linking childhood mental ability data to registers of psychiatric contact within a stable population in northeast Scotland. Data from a validated mental ability test administered to all 1921 born Scottish schoolchildren on June 1, 1932 were transformed into age-adjusted IQs. About 52.1% of those tested were identified as remaining in the region into adult life and 10.4% of these made contact with specialist psychiatric services by age 77. Odds ratios for the risk of psychiatric contact by IQ group were compared. A Cox regression analysis modeled the impact of socioeconomic deprivation, gender, and urban living. Intelligence is shown to be an independent predictor of lifetime psychiatric contact. Each standard deviation decrease in IQ results in a 12% increase in the risk of contact, independent of gender and childhood residence. The number of cases was too small to explore differences in diagnostic groups.