At EconLog Brad DeLong’s comments about IQ not being able to explain why rich parents have rich kids (prompting Fabio Rojas to say DeLong had discovered sociology) sparked the following from commenter Dr. T

DeLong’s argument shows ignorance of biology and statistics. The reason we do not see regression to the mean with IQ is that human procreation is not random. Few high IQ people have children with partners of below average IQ. If a person with a 140 IQ marries a person of 130 IQ, the likelihood that their child will have a 100 IQ is less than 5% (unless there is premature birth or brain damage).

I’m not an expert, but that sounded wrong to me. I said this in reply:

Even with non-random mating, we should still expect regression to the mean. If Andre Agassi marries Venus Williams, their kids are probably not going to be as good at tennis as they were, even though they will likely be better than average. Both people are flukes, statistically unlikely outliers in the field (by that I mean tennis ability in the general population). In the random pairing of genes that will produce their children, it is unlikely lightning will strike yet again (though I admit that did basically happen with both Venus and Serena giving their folks a perfect batting average).

If people reading this are familiar with the concept, have I given an accurate description of how regression to the mean works?

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