What IQ is linked to
IQ scores predict some things in life surprisingly well and others only weakly. Here's what large studies find.
These links are correlations, measured from 0 (no link) to 1 (perfect link). A correlation describes a trend across thousands of people. It doesn't decide any one person's life, and it doesn't show that IQ is the cause.
| Outcome | Typical link |
|---|---|
| School exam results | Strong (about 0.5; up to 0.8 in some studies) |
| Years of education | Strong (about 0.55) |
| Job level | Moderate (about 0.45) |
| Job performance | Moderate (about 0.3) |
| Income | Weak to moderate (about 0.2) |
School and education
The strongest link is with schooling. In a study of about 70,000 English children, ability measured at age 11 was closely tied to exam results at 16. Across many studies, IQ also predicts how long people stay in education.
Work and money
IQ is linked to the kind of job people end up in and, more weakly, to how well they do it. Older reviews put the link with job performance around 0.5; a 2022 re-analysis argued it's closer to 0.3. The link with income is smaller still: plenty of other things, such as family background, health, effort and luck, matter a lot.
Health and long life
People who scored higher as children tend, on average, to live longer. A review of studies following people for decades found that a 15-point higher childhood score went with about a 24% lower risk of dying during follow-up. Likely reasons include education, safer jobs and better use of health information.
Stability over a lifetime
Scores are fairly stable in adults. Scottish children tested at age 11 in 1932 were retested in their late 70s and 80s; their two scores correlated at about 0.6 to 0.7. That's stable, but far from fixed.
Genes and environment
Twin studies find that differences in IQ between people are partly genetic, and the genetic share grows with age: from roughly 40% in childhood to around 60% or more in adulthood. Environment matters too, especially in childhood. The large rise in scores over the 20th century (the Flynn effect) happened far too fast to be genetic.
Sources
- Deary, I. J., Strand, S., Smith, P. & Fernandes, C. (2007). Intelligence and educational achievement. Intelligence, 35(1).
- Strenze, T. (2007). Intelligence and socioeconomic success: A meta-analytic review of longitudinal research. Intelligence, 35(5).
- Schmidt, F. L. & Hunter, J. E. (1998). The validity and utility of selection methods in personnel psychology. Psychological Bulletin, 124(2).
- Sackett, P. R. et al. (2022). Revisiting meta-analytic estimates of validity in personnel selection. Journal of Applied Psychology, 107(11).
- Calvin, C. M. et al. (2011). Intelligence in youth and all-cause-mortality: systematic review with meta-analysis. International Journal of Epidemiology, 40(3).
- Deary, I. J. et al. (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).
- Haworth, C. M. A. et al. (2010). The heritability of general cognitive ability increases linearly from childhood to young adulthood. Molecular Psychiatry, 15.