I remember reading (I don't know where) that a child with an I.Q. of 130 (or whatever, 130 would be about 2 SDs) is as different from a child with an average I.Q. of 100 as an average child is from a child with an I.Q. of 70 (2 SDs below average - below which used to be defined as "retarded").
I'm willing to be corrected on this, but I think this is a very silly argument. First off, just on the surface it seems to defy common sense. Second, I.Q. tests are normed to create a normal distribution. That doesn't mean that what they are trying to explain when they measure "intelligence" is actually normally distributed. IOW, I.Q. is designed to be normally distributed, but that doesn't mean intelligence is.
Frankly, I was really surprised to see this statement in a published source but maybe I'm missing something. I look forward to seeing other opinions.
