Parental income and IQ among teens

Here's a new study of a large sample of teens published in Personality and Individual Differences that shows that the IQs of children from wealthy homes are higher, not because of money, but because of their parents' superior genes.

Parental educational level and family income have been related to individual differences in intelligence. However, large and representative samples are hardly available. Here two samples of young and old adolescents totaling 3233 boys and girls completed an intelligence battery comprising abstract, numerical, verbal, mechanical, and spatial reasoning subtests. Parents’ educational levels, family incomes, and adolescents’ general intelligence (g) were simultaneously related using SEM (structural equation modeling) analyses. The main findings show that (1) parental education strongly predicts family differences in income, (2) family income is not related to adolescents’ intelligence, and (3) parents’ education predicts adolescents’ intelligence regardless of family income. Because it is widely acknowledged that personal intelligence is the best predictor of educational differences, the next causal chain is endorsed: brighter parents reach higher levels of education, which allows approaching better occupations, and, therefore, they can create families with higher incomes. Adolescents from more affluent families tend to be brighter because their parents are brighter, not because they enjoy better family environments.

More on the IQ regression to the mean

In the recent post on IQ regression to the mean, reader Levi Johnston asked if there were enough black respondents to calculate IQs for those with two highly educated parents, not one or two. The n for blacks drops from 47 to 16--a small sample, indeed--but the results are a mean of 109.6 for whites and 105.3 for blacks (the difference is not statistically significant). Compared to the earlier results, scores went up a couple points for whites but five points for blacks. The gap in standard deviation (sd) terms shrunk from around half to about three-tenths.

I should note that with the full sample of blacks and whites, the IQ gap based on the GSS vocabulary test in only about 10 points--not the usual 15. This is probably due to the fact that the test taps verbal IQ, a form of intelligence with a smaller racial gap. For the full sample, the black-white difference is only two-thirds of an sd--not the one sd difference that researchers usually observe when looking at general intelligence.

Regression to the mean with GSS data

Do black and white adult children of parents who attended graduate school have the same average IQs? Why shouldn't they? They had the same advantages that come from growing up in a home of highly educated parents.

Using GSS data, I calculated mean IQs (based on a vocabulary test) for blacks and whites whose mothers or fathers completed at least 17 years of schooling (20 years is the highest possible score).

Mean IQ (N = 546)

Has highly educated mother
White 107.0
Black 99.5*

Has highly educated father
White 107.6
Black 99.7*


* significantly lower than white counterpart

Even though these folks have equally educated parents, there is a gap between them that is roughly half of a standard deviation--a fairly large difference.

Our results fit just about perfectly a regression to the mean equation where heritability for IQ is set at 0.5; the mean IQ for educated parents is set at 115; and the means for the white and black populations are set at 100 and 85, respectively.