Wolfgang, Income does not even come close to a normal distribution. It would be a "J" curve (with a fixed bottom and a theoretically infinite top), so the mean, median and mode are quite different.

IQ tests were designed and standardized to be normally distributed, which is why the actual distributions do approximate a normal curve if the tests are given to people representative of the standardization sample.

However, the tests do not get restandardized every five years or so, and scores of people in the US in general have tended to rise over the years, so that, if my memory serves me, the average (mean and median) IQ of children in the US is now over 100. (I have not kept up with the latest research on this, so I'm not sure of the specifics.)

Dr. J