Wednesday, February 06, 2008

Mom's IQ and family size: I analyzed data on more than 2,500 American women to look at the relationship between IQ and completed family size. Here are the mean number of children for women age 40-50 averaged within various decades:

Mean number of children

Low IQ
70s 3.84
80s 3.30
90s 2.49
00s 2.33

Medium IQ
70s 3.44
80s 2.76
90s 2.13
00s 2.03

High IQ
70s 2.96
80s 2.23
90s 1.68
00s 1.74

Not surprisingly, completed fertility has fallen over recent decades, and it has done so across all three IQ groups. Unfortunately, during any given period the smartest women have the fewest kids. There is one bit of encouraging news (highlighted in red): the only reversal in the above table is that high-IQ women ended up with more children in this decade than in the 1990s. Evidently, placing top priority on a career has slipped a little.

Update: I compared the mean number of children had by native-born Americans versus immigrants in this decade and found 1.68 and 2.29, respectively. So, fertility went up among smart women in America only because of the high numbers among immigrants.


  1. "Unfortunately, during any given period the smartest women have the fewest kids."

    Not to worry, No Child Left Behind will counteract the implications of this trend.

  2. dearieme2:42 PM

    Would you like to look at how old they are when they bear their children? I suspect that the low IQ women manage to sneak in a whole generation more of, ahem, generation, per century.

  3. What happens when you break the IQ categories by race? Are the changes in the low and medium group due to more hispanics?


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