Six Sigma and Beyond: Statistics and Probability, Volume III
Sampling histograms that are symmetric and without outliers can be converted to standardized random variables :
which has (1) mean of r.v.Z k at the origin: Zbar = 0; and (2) variance of r.v. Z k of any unity:
This standardized form of the sample r.v. conveniently presents results in terms of the number of standard deviations above or below the mean. This number is often called the "Z-score" and appears as:
A typical pictorial view of this type of distribution is shown in Figure 16.7.