1528 California children with IQs of 140 or higher were followed into adulthood in order to assess the importance of IQ in adult success and adjustment. The mean IQ of those that married and had children was 152; that of their spouses, 125. The mean IQ of this whole group of parents was 138.5. The mean IQ of 1571 of their children was 133.2, a little less than the parents and showing some regression to the mean.
These results show very little regression -- less than would be predicted from the estimates given in my earlier post. However, I suspect a correction needs to be applied as the Terman study was done before the Flynn Effect was understood. If the same version of the Stanford Binet was used on the parents and children, without Flynn re-norming, then the children were not as exceptional as implied by the 133 average given above. If we take the Flynn Effect in mid-20th century America to be about 10 points per generation (this is just a rough guess), then the 133 should be corrected to about 123, and is pretty consistent with the estimate I gave of: 100 + .6(38.5) = 123, which assumes narrow sense heritability h^2 = .6.
The discussion by Eysenck uses higher heritability numbers (note the non-negligible V_CE = variance due to common environment). If the Terman study used re-normed tests then their data would be evidence for much less regression than in my estimates.
