Monday, May 26, 2008

Strong Mind, Strong Body: IQ and Health

The ancient Greeks glorified "a strong mind in a strong body." A neat article by Linda Gottfredson, "Intelligence: Is It the Epidemiologists’ Elusive 'Fundamental Cause' of Social Class Inequalities in Health?" (2004. Journal of Personality and Social Psychology 86(1): 174–199) argues that strong minds are a major cause of strong bodies. Gottfredson begins with an excellent primer on why it's puzzling that - all over the world - the rich continue to live longer than the poor:
Age-specific rates of illness and death are often two to three times higher for individuals in the lower social strata. For many years the so-called poverty paradigm has dominated thinking about why such disparities exist. Under this paradigm, the disparities are presumed to result from differences in access to health care and other such resources... The poverty paradigm has foundered, however, on a growing number of contrary facts and vexing paradoxes, many of them pointed out decades ago...
Prominent among the challenging facts is that the paradigm’s key health resource—greater access to medical care—has surprisingly little relation to differences in health. The introduction of Medicaid and Medicare in the United States during the 1960s soon led to the poor making as many physician visits per year as the nonpoor, but large class differentials in health remained—even when the poor began to visit physicians at a higher rate than the nonpoor... Great Britain and other countries that had expected to break the link between class and health by providing universal health care were dismayed when the disparities in health not only failed to shrink but even grew...
So what gives? Gottfredson argues that social class is actually a mask for IQ. Interesting claim: "successively better surrogates for g [general intelligence] — income, occupation, education, health literacy—are successively stronger correlates of health outcomes."
Why would IQ lead to better health? Gottfredson puts forward a bunch of possibilities, but they mostly boil down to: Smart people choose healthier lifestyles, and get more benefit (and less harm) from medicine:
Patients cannot be passive recipients of medical recommendations with which they merely comply. Rather, many illnesses require the active participation of patients for proper diagnosis and treatment. We are our own primary providers of health care. This is especially true for chronic illnesses such as asthma, diabetes, and hypertension, because they require extensive self-regulation, which includes prevention, attack management, and social skills in maintaining social support...
These chronic conditions are similar to jobs that require considerable knowledge for good performance, but, because conditions keep changing, the jobs cannot be routinized. Like such jobs, chronic diseases therefore require constant judgment in applying old knowledge and the need to spot and solve new problems. They require the daily exercise of g. Not just g, but always g to some extent.
Chronic lack of good judgment and effective reasoning leads to chronically poor self-management.
All very interesting, though when I used the General Social Survey to race the predictive power of income, education, and IQ for subjective health, IQ came in third. How would Gottfredson explain that?