Process Analysis - Process (Machine) Capability Analysis - Testing the Normality Assumption

The indices we have just reviewed are only meaningful if, in fact, the quality characteristic that is being measured is normally distributed. Process Analysis provides a specific test of the normality assumption (Kolmogorov-Smirnov and Chi-square test of goodness-of-fit); these tests are described in most statistics textbooks, and they are also discussed in greater detail in Nonparametric Statistics.

A visual check for normality is to examine the probability-probability (P-P) and quantile-quantile (Q-Q) plots for the normal distribution. For more information, see Process Analysis and Non-Normal Distributions.