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Correlation between countries’ diseases and IQ

July 6, 2010

Researchers from the University of New Mexico have published a report that shows the negative correlation between national average IQ scores and the “disease burden” that countries face. The correlation is nearly 70%. Cambodia came out somewhere in the middle, with an average IQ of 91, and a disease burden rating of 4.1. El Salvador and Uganda had average IQs of 80 and 96 and disease burden ratings of 3.42 and 4.46, respectively.

Here’s how the disease burden was calculated:

As a measure of infectious disease levels for each nation, disability-adjusted life years lost (DALY) owing to infectious disease were used (WHO 2004b). This measure combines years of life lost and years spent disabled owing to 28 representative and important human diseases, including tetanus, malaria, tuberculosis, hepatitis, syphilis and leishmaniasis, such that one DALY equals one healthy year of life lost per 100 000 people. Although other cross-national measures of disease exist, we believe this to be the best for our study because (i) data exist for most countries of the world (n = 192), and (ii) this variable is a reasonable measure of the physiological costs of infectious disease, which concerns the parasite-stress hypothesis applied to cognitive ability.

The authors suggest that intelligence is most vulnerable to bouts of childhood diarrhea:

The host must activate its immune system to fight off the infection, at energetic expense. Of these, diarrhoeal diseases may impose the most serious cost on their hosts’ energy budget. First, diarrhoeal diseases are the most common category of disease on every continent, and are one of the two top killers of children under five, accounting for 16 to 17 per cent of all of these deaths worldwide (WHO 2004a). Second, diarrhoea can prevent the body from accessing any nutrients at all. If exposed to diarrhoeal diseases during their first five years, individuals may experience lifelong detrimental effects to their brain development, and thus intelligence.

The usual criticisms of IQ as the most appropriate measure of intelligence cannot be overlooked. Given the history of IQ tests as being used for scientifically-supported racism and the questionable feasibility of accurately measuring abstract intelligence with a simple number, I want to take these results with a grain of salt.

But their findings actually undermine the racist conclusions drawn by worldwide IQ test results. And they add credence to a model of holistic health, with international statistics and medical explanations to back them up. Check out The Economist for a good summary of how the correlation established here could be used to suggest causality.

Teaching about handwashing just got a little important to me.

h/t Duncan Green, From Poverty to Power

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