Whoa Nelly! In a very interesting ask-a-researcher thread on Pschological Comments, researcher Michael A. Woodley drops the following, which surprised me a fair bit. The context is that there is intergenerational regression to the mean in intelligence. That is, very smart parents tend to have children who are less smart than they are; very dull parents tend to have children who are less dull than they are. Or so I thought - and not just I, I'm sure. Woodley disagrees. He quotes from a book by himself and Aurelio Jose Figueredo. Here's the central bit:
Furthermore in the case of parent-offspring correlations on g, oversampling parental scores with positive errors of measurement on IQ, as by selecting those identified as high-g individuals based on high observed IQ scores for special study, will produce regression to the mean when assessing the IQ of their offspring, even if the offspring were genetically identical to the parents, given the nature of this statistical artifact. This can be confirmed by retesting the parents themselves, which is rarely done, because one will then no doubt observe regression to the mean of the parental IQ scores in the parents themselves, presumably without having undergone any genetic recombination whatsoever. The proposition that offspring are necessarily closer to the mean of the general population in their actual latent g-factor (as opposed to their observed IQ scores) is therefore a fallacy, especially under conditions of assortative mating.
Quite a claim. Is this generally accepted, or perhaps Woodley & Figueredo's minority position? When they say that the claim "can be confirmed by retesting the parents themselves, which is rarely done", does this mean it has been done? Repeatedly?
This would explain a puzzle, though: If there were regression to the mean in a substantial sense, then it should not be over after a generation, which would mean that, by now, we should all be pretty much equally intelligent, right? With the above interpretation, that problem does not exist.
I just hope he means to restrict his statements about the nonexistence of regression to the mean to the context at hand. The phenomenon is certainly real in other contexts - unless you want to redefine, for example, a particularly hot day in a certain city as just an expression of a city's underlying latent hotness measured with upward error, and the like.