The Evolution of Pearson's Correlation Coefficient

This article describes an activity for developing the notion of association between two quantitative variables. By exploring a collection of scatter plots, the authors propose a nonstandard "intuitive" measure of association; and by examining properties of this measure, they develop the more standard measure, Pearson's Correlation Coefficient. The activity is designed to help students better understand how statistical measures are "invented" and why certain measures are preferred.