Galton’s Bend: An Undiscovered Nonlinearity in Galton’s Family Stature Regression Data and a Likely Explanation Based on Pearson and Lee’s Stature Data

In Francis Galton’s 1886 paper “Regression Towards Mediocrity in Hereditary Stature,” Galton analyzed the heights of 928 adult children and their 205 pairs of parents to illustrate his linear regression model. Although Galton’s data have been recalled frequently to illustrate linear regression and regression toward the mean, no one seems to have noticed that his height data do not fit his model. The purpose of this paper is both to reveal this curiosity and to find a possible explanation for its existence using related data from Galton’s colleague Karl Pearson