⁴ When playing with any sort of data set, if you randomly draw one value and obtain one that is extremely far from the mean (that is, the average value), the next one that you draw will probably be closer to the mean than even further away from it. Regression toward the mean was first described by Sir Francis Galton in the late nineteenth century, but under a slightly different name: regression toward mediocrity. Galton observed that parents who were very tall tended to have children who were shorter than they were and that parents who were very short had children who were taller than them. Galton said that extreme traits tended to “regress” toward “mediocrity.” His paper is available online, and it’s a delight: http://galton.org/essays/1880-1889/galton-1886-jaigi-regression-stature.pdf.