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Friday, March 13, 2009

Higher IQ = Longer Life? Yes, say Swedish.

ResearchBlogging.orgThe Swedish do all the cool studies. I don't know what it is lately - every study I find that piques my interest seems to be of Swedish men.

Anyhow, we've already looked at whether your name affects your income, how about your IQ affecting your longevity?

A study of 1 million (yes, million) Swedish men has found a strong link between IQ scores in adulthood and mortality.

Apparently, one of the major causes of death is unintentional injury - things like poisonings, fire, falls and drownings. It's the leading cause of death for people under 45 years old. The study was done in Sweden because they, as it turns out, keep meticulous records on their populace. Like in the US, men have to register for a military draft, but in Sweden they take IQ scores when they do, which when combined with birth, death, and housing/census records means just about every able bodied man in the country has his age, health, socioeconomic status, cause of death and IQ recorded in accessible data. This gave the researchers a uniquely complete set of data to work with.

Figure 1. IQ and selected injury mortality
(N = 1,116,442), Sweden, 1969–2004. Gray bars,
age adjustment; black bars, full adjustment
(without education); white bars, full adjustment
(with education). Referent: highest-scoring IQ group
(category 9). A) All injuries (n = 5,415); B) road injury
(n = 2,876); C) poisonings (n = 531).

The scientists observed that in previous studies, the risk of fatal accidental death was much higher for those with low socioeconomic status. IQ, as it turns out, is also positively correlated with class - which makes sense, since those with more financial means are more likely to live in areas with better schools and/or afford a better education. So, logically, the researchers wanted to know if the two might be related - that is, lower IQs leading to more accidental deaths.

The results were clear. Those with lower IQs were significantly more likely to have died via accidents like falling or drowning than their 'smarter' peers. Compared with those in the highest IQ category, men in the lowest-scoring IQ category had a death rate from unintentional injury which was more than twice as high - almost six times as high for poisoning. The trend continued even when they corrected for economic class - that is, the stupid rich people were still more likely to die than the smart poor people, suggesting that the intelligence, not their financial situation, was a contributiong cause of their deaths. Of course, economic class still was a factor, but at least 19% (and as high as 86%) of the variation in risk could be attributed to differences in IQ.

Not that any of this is terribly surprising - it's just very interesting that its shown in such a large study. It's rare to have data for over a million men. Other studies with far fewer subjects have found similar results. One of the main reasons this correlation might exist between IQ and death has to do with access to healthcare. Higher intelligence leads to better jobs and thus better healthcare - those who make less and have either poor or no healthcare are more at risk of dying when something goes wrong. It's also possible that the job type is an important variable - those with higher IQ are able to attain more intellectual jobs, like academia, which are generally lower in accident risk than manual labor jobs, like working in a factory.

The other important finding of this study is that there was one variable that had a significant impact on risk despite IQ - education. So getting an education lowered the risk of fatal accidental injuries independent of IQ. This means that those who aren't the sharpest tool in the shed can still lower their risk of impaling themselves on one by working hard and getting through high school and college. Now if that's not a reason to stay in school, I don't know what is.

Batty, G., Gale, C., Tynelius, P., Deary, I., & Rasmussen, F. (2008). IQ in Early Adulthood, Socioeconomic Position, and Unintentional Injury Mortality by Middle Age: A Cohort Study of More Than 1 Million Swedish Men American Journal of Epidemiology, 169 (5), 606-615 DOI: 10.1093/aje/kwn381

11 comments:

Anonymous said...

Health care may be an important factor in other studies, but not this one. This is Sweden, not the US - they all have access to high quality health care!
- Anne

liliannattel said...

That was interesting--I was wondering as I read it how socioeconomic class played into it and that question was answered. The point that education has an effect independent of IQ is a really important one. The one unanswered question is how the measure of IQ itself is affected by class, ie how good a measure of intelligence is it.

WhySharksMatter said...

Could some of this be because many high IQ people are nerds who play on the computer instead of playing outside? You're not terribly likely to drown if you don't go near the water. Interesting article.

G.D. said...

WhySharksMatter:

I don't have the references right now, but in fact the opposite is true - people from higher socioeconomic classes are far more physically active than people from lower classes. In fact, the best predictor for physical activity is education, and the best predictor for spending much time in front of the TV or computer is low education.

Johan said...

"This means that those who aren't the sharpest tool in the shed can still lower their risk of impaling themselves on one by working hard and getting through high school and college"

That is assuming that the correlation in fact is causation which is a pretty strong assumption in this case, considering the lack of obvious casual mechanism.

Dawn said...

"Higher intelligence leads to better jobs and thus better healthcare - those who make less and have either poor or no healthcare are more at risk of dying when something goes wrong. It's also possible that the job type is an important variable - those with higher IQ are able to attain more intellectual jobs, like academia, which are generally lower in accident risk than manual labor jobs, like working in a factory."

I disagree. Higher intelligence might or might not lead to a better job with better benefits and more frequent access to healthcare. Higher intelligence more probably leads to an overall higher self-awareness, which may lead to better self-care.

Also, IQ has less to do with career choices and socioeconomic class than what you've presumed. My IQ, for instance, is 153; I've never made more than $25K/year. (Of course, I've never worked in a factory, either. If I had, I would've made much more than that, even working on the factory floor rather than in management). I've read of or know personally of enough similar examples to throw a good bit of (personal) doubt on such a correlation.

But this was an interesting post!

Christie Lynn said...

Johan: The causal mechanism, presumably, would be that higher intelligence means you are more able to recognize and avoid hazards

Dawn: The correlation between IQ and Socioeconomic class is supported by research - it's not my assumption. As with any connection, there are always exceptions - that's why it was so interesting that they found the connection between IQ and hazards even when socioeconomic class was taken into account.

Johan said...

"The causal mechanism, presumably, would be that higher intelligence means you are more able to recognize and avoid hazards"

Yes, that is possible but I was specifically referring to the claim that more education would help regardless of IQ. As I said, that is assuming correlation = causation.

Stephanie B said...

Discussions like this are interesting intellectually, but I'm not sure they mean much without a thorough understanding of all the factors that could be contributors. As Johan noted, a correlation and a cause are not necessarily one and the same. Nor, for that matter, are education and actual intelligence, though I suspect that education and IQ are more likely to coincide in cultures where socioeconomic factors are less likely to preclude higher education.

Testing "IQ" absolutely is not an exact science and it tends to acknowledge education as much as native intelligence, if you know what I mean. Education and a willingness to learn can greatly reduce accidents and a good logical ability can preclude accidents. Both can also encourage you to avoid unhealthy habits and take up healthy ones.

An example, for instance: When I was in college, smoking was all but unknown in the engineering and physics buildings and not so in the humanities. I wonder how much education and smoking habits are reflected in this study.

Which goes to show there could be any numbers of other factors not readily observed.

DrBurst said...

Someone needs to tell them that a sample size over 40 is significant enough. A sample size of 1 million would be hyper-accurate. The sample size is so high, they don't have to worry about making your sample random or having a normal distribution. Just by looking at the sample size, these results are indisputable.

Rebecca said...

I think that smarter people can think ahead or project the outcome of their actions better than not -so-smart people.
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