Friday, November 14, 2008

IQ and longevity

IQ predicts longevity, even after controlling for social class.

A 12 minute test administered to an 11 year old predicts longevity better than (adult) body mass index, total cholesterol, blood pressure or blood glucose, and at a similar level to smoking.

If you don't like the 12 minute Wonderlic test ("culturally biased!"), you can try the entirely abstract Raven's Progressive Matrices, which are even more g-loaded than the Wonderlic.

In the studies described below they most likely didn't use either the Wonderlic or RPM, but the results of all well-designed IQ tests are highly correlated.

Nature: Ten years ago, on 16 October 1998, I presented findings that people from Aberdeen with higher childhood IQs — measured at age 11 in the Scottish Mental Survey of 1932 — were significantly more likely to survive to age 76. It was at a psychology seminar at Glasgow Caledonian University, UK. For one audience member, the finding did not go down well. "So, you're saying that the thick die quick?" It was not a point of clarification; it was an accusation. The temperature in the room rose as the questioner railed against a result he found insulting and wanted to invalidate. Hadn't intelligence tests been discredited?

Actually, no. Scores from cognitive-ability tests (also known as intelligence tests or IQ tests) have validity that is almost unequalled in psychology [1]. A general cognitive-ability factor emerges from measures of diverse mental tasks, something that hundreds of data sets since 1904 have replicated. People's rankings on intelligence tests show high stability across almost the whole lifespan, are substantially heritable and are associated with important life outcomes — including educational achievements, occupational success and morbidity and mortality. More thumping confirmatory studies of the link between intelligence and mortality have appeared since our first work. One of these contains nearly a million Swedish men tested at around age 19 during military induction and followed for almost 20 years [2]. It shows a clear association: as intelligence test scores go up the scale, so too does the likelihood of survival over those two decades.

When we attempted to publish our original study, we came across a different complaint: the journals to which we submitted our initial findings said they found the link obvious. It was already well known that health inequalities are associated with different social backgrounds. That was deemed the likely explanation for the finding. But it has since been shown that childhood social class does not account for the association between childhood intelligence and later mortality [3].

Intelligence can predict mortality more strongly than body mass index, total cholesterol, blood pressure or blood glucose, and at a similar level to smoking
[4]. But the reasons for this are still mysterious. That needs to change. Reducing health inequalities is a priority, and to do that we need to determine their causes.

It's plausible that intelligence might have positive benefits for longevity, but it could also have turned out the other way around -- controlled experiments have shown in species such as C. Elegans (worms) and E. Coli (bacteria) that increased learning ability comes with fitness costs such as decreased disease resistance or physical capability. I wonder if the positive IQ--longevity correlation in humans persists even in the high tail.

(Via GNXP.)


Anonymous said...

IQ-longevity correlations is pretty obvious -- stupidity kills. What's more important is whether IQ correlates with number of offsprings. This is less obvious because academic success leads to extended education and delayed procreation and hence fewer offsprings per 100 years.

Unknown said...

Steve, Do you think there is a positive correlation between IQ and obsession with debating about IQ?

Kenneth Clark said...

I wonder how much intelegence correlates with extended education. One on the smartest persons I worked with at JPL (full of PHDs from Cal Tech, MIT, and Cornell) joined the USMC after high school and never took a college course.

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