The impact of childhood intelligence on later life: Following up the Scottish Mental Surveys of 1932 and 1947

70,805). These surveys are described. This research, using the surveys ’ data, examined (a) the stability of intelligence differences across the life span, (b) the determinants of cognitive change from childhood to old age, and (c) the impact of childhood intelligence on survival and health in old age. Surviving participants of the Scottish Mental Surveys were tested, and the surveys ’ data were linked with public and health records. Novel findings on the stability of IQ scores from age 11 to age 80; sex differences in cognitive aging; the dedifferentiation hypothesis of cognitive aging; and the effect of childhood IQ on all-cause and specific mortality, morbidity, and frailty in old age are presented. Scotland’s Mental Survey Committee gathered in 1931 to plan a study to describe the mental ability of the Scottish nation’s children (Scottish Council for Research in Education, 1933). They found no practicable method of obtaining a representative sample. They decided to test the whole nation. On Wednesday, June 1, 1932, practically every child attending school in Scotland and born in 1921 took the same mental test with the same time limit after hearing the same instructions. Thus Scotland was and remains the only nation with mental test data for almost an entire birth cohort. What is more, they repeated the exercise in 1947, testing almost al