Date of this Version
The American Statistician
A normal quantile-quantile (QQ) plot is an important diagnostic for checking the assumption of normality. Though useful, these plots confuse students in my introductory statistics classes. A water-filling analogy, however, intuitively conveys the underlying concept. This analogy characterizes a QQ plot as a parametric plot of the water levels in two gradually filling vases. Each vase takes its shape from a probability distribution or sample. If the vases share a common shape, then the water levels match throughout the filling, and the QQ plot traces a diagonal line. An R package qqvases provides an interactive animation of this process and is suitable for classroom use.
Education, diagnostic, simulation
Stine, R. A. (2017). Explaining Normal Quantile-Quantile Plots Through Animation: The Water-Filling Analogy. The American Statistician, 71 (2), 145-147. http://dx.doi.org/10.1080/00031305.2016.1200488
Available for download on Wednesday, June 06, 2018
Date Posted: 27 November 2017
This document has been peer reviewed.