Research Findings: Social class: Role of IQ in the relationship between social position and health Summary papers
Does IQ explain socioeconomic inequalities in health?
Explanations of variations in health inequalities have traditionally focused on access to resources (such as education and income), exposure to working and living environments (such as housing conditions and pollution), and health related behaviours (such as smoking and diet). It has recently been suggested by researchers that intelligence (as measured by IQ tests) may play a key role in social class inequalities in health.
This project focused on the oldest age cohort and looked at their socioeconomic position such as where they live, education, childhood and current social class, and income, against various health outcomes including heart disease, lung function and death. The greatest risk of ill health and death was found in the most disadvantaged groups. Participants took verbal and numeric IQ tests and we found that after adjusting for intelligence there was a significant reduction in risk for some health outcomes such as poor mental health, and heart disease. We concluded that although IQ does not completely explain socioeconomic differences in health it may contribute to them. This study adds further evidence in support of efforts to reduce inequalities in health that are based on educational opportunities and interventions particularly in early life.
Batty, D., G. Der, et al. (2006). "Does IQ explain socioeconomic inequalities in health? Evidence from a population based cohort study in the West of Scotland." BMJ 332: 580-4.
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Slower reaction times may link lower IQ with earlier death
More limited IQ is known to be associated with early death but the cause of the relationship is unknown. Here, we measured psychometric intelligence (IQ) and reaction times at baseline (1987) in the oldest cohort of the Twenty-07 Study who were then followed up with respect to survival until age 70.
We found both IQ and reaction times were significantly related to all-cause death rates. The association between IQ and death remained significant after adjusting for education, occupational social class, and smoking, all of which have been considered to be confounding factors. However, the effect of IQ on death was not significant after adjusting for reaction time. This suggests that reduced efficiency of information processing might link less able mental ability and earlier death. Our findings support strong evidence for the importance of psychological factors in physical health and human survival. Finding the mechanisms that relate IQ to death might help in formulating effective interventions to reduce inequalities in health.
Deary, I. and G. Der (2005). "Reaction time explains IQ's association with death." Psychological Science 16(1): 64-69.
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Reaction time, age and cognitive ability
There is much interest in age-related changes in the way people process information. Age-related differences in reaction times might account for variations in more complex cognitive functions such as reasoning, memory and spatial abilities. Earlier research as been largely based on biased population samples.
In this study, we tested simple and choice reaction times in the first wave (1987) when respondents were aged 16, 36, and 56 years. Participants were re-tested eight years later, at which time they also took maths test – the Paced Auditory Serial Addition Test (PASAT).
We found that simple and choice reaction times became slower and more variable with age. Women from age 36 to 63 showed more variability in choice reaction times than men. Reaction time differences largely accounted for age differences, but not sex differences in PASAT scores.
Deary, I. and G. Der (2005). "Reaction time, age, and cognitive ability: longitudinal findings from age 16 to 63 years in representative population samples." Aging, Neuropsychology and Cognition 12: 187-215.
Reaction times and intelligence differences
The association between reaction times and psychometric intelligence test scores is a major factor in the information-processing approach to mental ability differences. We examined the associations between scores on a test of general mental ability (Alice Heim 4: AH4 test) and reaction times in the oldest cohort of the Twenty-07 Study. This provided the first report of reaction time and psychometric intelligence in a large, normal sample of the population. It provided a benchmark for other studies and suggested larger effect sizes than the majority of previous studies, which have tended to be on young student samples.
Deary, I., G. Der, et al. (2001). "Reaction time and intelligence differences: a population based cohort study." Intelligence 29(5): 389-399.