Cognitive epidemiology

Cognitive epidemiology is a field of research that examines the associations between intelligence test scores (IQ scores or extracted g-factors) and health, more specifically morbidity (mental and physical) and mortality. Typically, test scores are obtained at an early age, and compared to later morbidity and mortality. In addition to exploring and establishing these associations, cognitive epidemiology seeks to understand causal relationships between intelligence and health outcomes. Researchers in the field argue that intelligence measured at an early age is an important predictor of later health and mortality differences.

A strong inverse correlation between early life intelligence and mortality has been shown across different populations, in different countries, and in different epochs."

A study of one million Swedish men found showed "a strong link between cognitive ability and the risk of death."

A similar study of 4,289 former US soldiers showed a similar relationship between IQ and mortality.

The strong correlation between intelligence and mortality has raised questions as to how better public education could delay mortality.

There is a known inverse correlation between socioeconomic position and health. A 2006 study found that controlling for IQ caused a marked reduction in this association.

Research in Scotland has shown that a 15-point lower IQ meant people had a fifth less chance of seeing their 76th birthday, while those with a 30-point disadvantage were 37% less likely than those with a higher IQ to live that long.

Another Scottish study found that once individuals had reached old age (79 in this study), it was no longer childhood intelligence or current intelligence scores that best predicted mortality but the relative decline in cognitive abilities from age 11 to age 79. They also found that fluid abilities were better predictors of survival in old age than crystallized abilities.

The relationship between childhood intelligence and mortality has even been found to hold for gifted children, those with an intelligence over 135. A 15-point increase in intelligence was associated with a decreased risk of mortality of 32%. This relationship was present until an intelligence score of 163 at which point there was no further advantage of a higher intelligence on mortality risk.

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