Last week, The Economist publicized some research by Christopher Eppig, a graduate student at the University of New Mexico. Eppig's research posits that the relationship between national disease burden and national IQ scores is causal, and that this decreased IQ level is thus a symptom, and not a cause, of underdevelopment in countries that lack health and hygiene infrastructures. The Economist summarizes how
Eppig and company reached their conclusion of causation (emphasis mine):
The correlation is about 67%, and the chance that it might have come about at random is less than one in 10,000. But correlation is not causation, so Mr Eppig and his colleagues tried to eliminate other possible explanations. Previous work has offered income, education, low levels of agricultural labour (which is replaced by more mentally stimulating jobs), climate (the challenge of surviving cold weather might provoke the evolution of intelligence) and even distance from humanity’s African homeland (novel environments could encourage greater intelligence) as explanations for national differences in IQ. However, all of these, except perhaps the last, are also likely to be linked to disease and, by careful statistical analysis, Mr Eppig and his colleagues show that all of them either disappear or are reduced to a small effect when the consequences of disease are taken into account.Wow! They accounted for a lot of different stuff there! Do you think they accounted for every possible confounding factor? (Not possible!) It's also certain that the previous work they rely on included major ambiguities and assumptions in itself. And did you notice that the authors included distance from Africa as a cause for increased intelligence? It's like magic! Or really crappy analysis. I expected them to throw in craniometry as a potential confounding factor for good measure.
Now, a longstanding complaint of mine is that The Economist doesn't rigorously source articles, making it difficult for readers to go back to the studies and decide for themselves. Sometimes (oftentimes?) journalists don't understand a correct / responsible way to interpret data. So here's the full text of Eppig's article as published in Proceedings of the Royal Society.
First of all, I take issue with the scientific measurement of intelligence on such a broad, multi-cultural scale. Like love, joy, or pain, intelligence is something that is really difficult to define. And like, IQ tests, how bullshitty are those? Perhaps it is true that intelligence would vary on a national level - but I suspect that you would find even greater variance in definitions of intelligence across cultures. Even within our own culture, how would you describe a star mathematician, brilliant actor, and shrewd politician in a way that classified them all as equally intelligent.
