> for a wide class of probability distributions, no more than a certain fraction of values can be more than a certain distance from the mean. Specifically, no more than 1/k^2 of the distribution's values can be k or more standard deviations away from the mean.
IQ is (if I recall correctly) normally distributed with a standard deviation of 15. So for a distance of 1.3... standard deviation (i.e. a distance of 20), you can't have more than 1/1.3...^2 = 56.25% of the population so far from the mean (below 80 or above 120), or 28.125% _above_ 120.
> for a wide class of probability distributions, no more than a certain fraction of values can be more than a certain distance from the mean. Specifically, no more than 1/k^2 of the distribution's values can be k or more standard deviations away from the mean.
IQ is (if I recall correctly) normally distributed with a standard deviation of 15. So for a distance of 1.3... standard deviation (i.e. a distance of 20), you can't have more than 1/1.3...^2 = 56.25% of the population so far from the mean (below 80 or above 120), or 28.125% _above_ 120.