Not sure if you're kidding, but GP is referring to area of the one-sigma region around mean for a normal distribution (see: bell curve) in relation to the total

Not sure if you're kidding, but GP is referring to area of the one-sigma region around mean for a normal distribution (see: bell curve) in relation to the total area (68ish percent of total), which is usually where the "normal" people live. It seems the popular understanding in soft sciences is that distribution of talent/ability/other human metric seems to follow a normal distribution.