Abstract
AbstractNumerous studies find a positive relationship between cognitive ability, IQ as measured in childhood or youth, and subsequent survival. Explanations range from the idea that low ability is an indicator of adverse systemic events in early life to the idea that high cognitive functioning is required continuously to maintain health and reduce threats to survival. The Wisconsin Longitudinal Study (WLS) has followed a large cohort of Wisconsin high school seniors from ages 18 to 69. As expected, in the WLS survival varies positively with adolescent IQ. However, rank in high school class accounts completely for the relationship between IQ and survival, and it has a much larger effect on survival. These findings suggest that cognitive functioning improves survival by promoting behaviours that boost health status, minimize exposure to known risks and optimize returns to health producing inputs, and that such behaviours are firmly in place by late adolescence.
Highlights
In a large American sample of high school graduates the association between early IQ and survival from ages 18 to 69 is entirely explained by a measure of academic performance that is only moderately associated (r = 0.6) with IQ
The effect of rank in high school class is about three times larger than that of IQ. This finding suggests that higher cognitive functioning improves the chances of survival because it leads to behaviours that are responsible, well organized, timely, and appropriate to the situation, and such patterns of behaviour are well established by late adolescence
Research on the association between early IQ and survival has led to the development of a nascent subdiscipline, cognitive epidemiology[4,5,6,7,8,9]
Summary
Numerous studies find a positive relationship between cognitive ability, IQ as measured in childhood or youth, and subsequent survival. Consider the recent paper in which Batty et al.[11] estimated the relationship between IQ (military induction test) and mortality among 1 million Swedish men for approximately 20 years (from roughly age 18 to age 38) Their main finding is a highly significant hazard ratio of 1.32 for the association between a one standard deviation difference in IQ and the likelihood of death. In addition to estimating the vector of parameters, β, along with ρ and γ, we calculated the predicted integrated hazard, I(y; β, ρ, γ ), for selected subgroups (setting all the variables not defining the subgroups to their sample mean) and the probabilities of surviving S(x; β, ρ, γ) = exp(-I(y; β, ρ, γ ), and the expected duration in the intervals (x, 68) for all x between 18 and 67 The latter quantities are much better measures of the ultimate effects of selected covariates than the vector, β, or the relative hazards, exp(β)
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