Explaining Normal Quantile-Quantile Plots Through Animation: The Water-Filling Analogy |
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Authors: | Robert A Stine |
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Institution: | Department of Statistics, The Wharton School, University of Pennsylvania, Philadelphia, PA |
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Abstract: | 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. |
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Keywords: | Diagnostic Education Simulation |
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