The science of intelligence
Intelligence and health
Short answer
In large studies, people who scored higher on cognitive tests early in life tended to live longer. A meta-analysis of 16 studies and over 1.1 million people found that a 1 standard deviation advantage (15 points on the IQ scale) went with a 24% lower risk of death over 17 to 69 years. It is a group pattern, not a personal forecast.
Want your own number? The test is 25 visual puzzles, about 12 minutes, no sign-up.
Where the evidence comes from
Research linking intelligence and health is sometimes called cognitive epidemiology. It depends on a rare kind of data: intelligence scores from childhood, matched to health records decades later. Scotland supplied some of the best. The Scottish Mental Surveys tested almost everyone born in 1921 and 1936 who was at school on the survey days, 89,498 children in 1932 and 70,805 in 1947 (Deary et al., 2004). Because nearly a whole birth year was tested, later follow-ups could compare people across the full range of ability rather than a selected group.
The main finding: lifespan
A 2011 meta-analysis combined 16 studies with 1,107,022 participants and 22,453 deaths. A 1 standard deviation advantage in early-life cognitive test scores was associated with a 24% lower risk of death over 17 to 69 years of follow-up (Calvin et al., 2011). On the IQ scale, 1 standard deviation is 15 points, the gap between 100 and 115.
A 24% lower risk is a relative figure. It compares the rate of death in two groups over the follow-up period; it does not mean higher scorers live 24% longer, and it says nothing about how many years any one person will live.
Try one · Pattern Recognition
Which tile comes next?
Tap the option you think is right, or show the answer.
Show the answer
The missing tile shows a very large outlined arrow pointing down and to the left (option 2).
How to solve it
- Compare neighboring tiles and name what changes each time.
- From tile to tile, the arrow turns an eighth of a turn counterclockwise.
- From tile to tile, the arrow gets bigger.
- Everything else stays the same from tile to tile.
- The last tile shows a large outlined arrow pointing left. Apply each change once more.
- So the missing tile shows a very large outlined arrow pointing down and to the left.
That was 1 puzzle. The full test has 25.
What explains the link?
The same meta-analysis tested some explanations by adjusting for other factors (Calvin et al., 2011):
| Factor adjusted for | Effect on the intelligence-mortality link |
|---|---|
| Childhood socioeconomic status | Almost no effect |
| Adult socioeconomic status | reduced by 34% |
| Education | reduced by 54% |
So the link is not simply a matter of being born into a wealthier family. A large part of it travels with what happens later: how much schooling people get and the kind of adult life they lead. That fits the wider pattern in which IQ correlates about .55 with years of education (Neisser et al., 1996), and about .45 with occupational level and .23 with income (Strenze, 2007). Those outcomes are covered in the IQ and life outcomes guide. What remains after adjustment is not explained by these studies.
Why childhood scores still mean something at 80
Childhood scores could only predict late-life outcomes if rank is fairly stable over time. In the Lothian Birth Cohort 1921, the same test at 11 and 90 correlated .54, or .67 after correction for range restriction (Deary et al., 2013). That stability is covered in intelligence across the lifespan.
The arrow points both ways
Health also affects thinking. Diamond's review of executive functions notes that stress, lack of sleep, loneliness or lack of exercise each impair them (Diamond, 2013). Those are the control skills behind planning and focus, described on the executive function page.
Caveats
- Association, not proof of cause. These are observational studies. They show that test scores and survival go together, not why.
- Group pattern. As the 1994 mainstream statement put it, a high IQ "no more guarantees success than a low IQ guarantees failure in life" (Gottfredson, 1997). The same holds for health.
- Not a personal forecast. No score, including an estimated IQ from an online test, can tell you how long you will live. See does IQ predict success? for the same point about careers.
Sources
- Deary, I. J., Whiteman, M. C., Starr, J. M., Whalley, L. J., & Fox, H. C. (2004). The impact of childhood intelligence on later life: Following up the Scottish Mental Surveys of 1932 and 1947. Journal of Personality and Social Psychology, 86(1), 130-147. doi.org/10.1037/0022-3514.86.1.130
- Calvin, C. M., Deary, I. J., Fenton, C., Roberts, B. A., Der, G., Leckenby, N., & Batty, G. D. (2011). Intelligence in youth and all-cause-mortality: Systematic review with meta-analysis. International Journal of Epidemiology, 40(3), 626-644. doi.org/10.1093/ije/dyq190
- Deary, I. J., Pattie, A., & Starr, J. M. (2013). The stability of intelligence from age 11 to age 90 years: The Lothian Birth Cohort of 1921. Psychological Science, 24(12), 2361-2368. doi.org/10.1177/0956797613486487
- Neisser, U., Boodoo, G., Bouchard, T. J., Jr., Boykin, A. W., Brody, N., Ceci, S. J., Halpern, D. F., Loehlin, J. C., Perloff, R., Sternberg, R. J., & Urbina, S. (1996). Intelligence: Knowns and unknowns. American Psychologist, 51(2), 77-101. doi.org/10.1037/0003-066X.51.2.77
- Strenze, T. (2007). Intelligence, 35(5), 401-426. doi.org/10.1016/j.intell.2006.09.004
- Gottfredson, L. S. (1997). Mainstream science on intelligence: An editorial with 52 signatories, history, and bibliography. Intelligence, 24(1), 13-23. doi.org/10.1016/S0160-2896(97)90011-8
- Diamond, A. (2013). Executive functions. Annual Review of Psychology, 64, 135-168. doi.org/10.1146/annurev-psych-113011-143750