One TGGP’s commentators, Jason Malloy, linked to this article on sex, status and reproductive success in the US by sociologist Rosemary Hopcroft. She finds that fertility generally declines as income, education and IQ increase but that the relationship is different for men and women. She reports that male fertility increases with income while female fertility decreases. Since income is usually positively correlated with IQ this association would be evidence against the “only stupid people are breeding” theory.
She used GSS data but modeled the relationship between fertility and other factors using an ordinary least squares regression. I think a generalized linear model with a Poisson distribution and a log link is more appropriate for count data so I down loaded the GSS data and repeated her analysis. I confirmed that the association of income and fertility is different in men and women (there is an interaction, p < 0.001) but I think the relationship is more complicated. A GLM was fit separately for each gender and had a main effects of age, age squared, WORDSUM score and income and there appears to be an interaction between WORDSUM and income. Low income is an effective birth control for smarter men but not for the dimmer (see graph). Intelligent poor men report the fewest children but the fertility of men with lower scores on the WORDSUM does not vary as much by income. This reminds me of a result in cognitive epidemiology. Having children when you have a low income may be viewed as a “disease” that men with higher intelligence avoid.
GSS variables used: INCOME (Family income in 1996 dollars), CHILDS, WORDSUM, SEX, AGE
6 comments:
Low income is an effective birth control for smarter men but for the dimmer (see graph)
Should that include a "not"?
Yes. Thanks.
Wouldn't be better to use RINCOM98? INCOME aims to be fine-grained at the low end, but RINCOM98's highest category is $110K+.
Ron,
Thanks for the tip. I will rerun the analysis later.
Regardless of income, no group is averaging 2+ kids per man.
Very interesting and good to see a study of men. It might yield different results if you used men aged 50. Men who are at least 50 are more likely to have had all their children even if the wife is 10 years younger. Even though I married young (21) my husband was older so he was 38 for the first baby and 46 for the 2nd. He would have zero kids on your chart. Don't know his wordsum score but I would guess at least 8 if not 10.
My point is you could miss many on the right side by having a cutoff that is too young. Plenty of successful men marry later to younger women.
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