Originally Posted by Bostonian
It's not, because the number of children with IQ >= 130 from a certain group depends on the average IQ of children in the group. If the average IQ of children of college gradutes is 115, a much higher fraction of them will be gifted than the children of parents who did not go beyond high school. In other words, the entire distribution of IQ in some groups is shifted toward the right, and in other groups shifted toward the left, which has implications for the incidence of giftedness.

This argument is a solid demonstration of innumeracy. Whether the gifted population in your sample is 1 in 50 or, let's say, 1 in 10, the group still isn't large enough to significantly influence averages.

Also, you're now excluding gifted people who don't graduate college.