PROBPLOT Statement

Overview

The PROBPLOT statement creates a probability plot, which compares ordered values of a variable with percentiles of a specified theoretical distribution such as the normal. If the data distribution matches the theoretical distribution, the points on the plot form a linear pattern. Thus, you can use a probability plot to determine how well a theoretical distribution models a set of measurements.

You can specify one of the following theoretical distributions with the PROBPLOT statement:

beta
exponential
gamma
three-parameter lognormal
normal
two-parameter Weibull
three-parameter Weibull

You can use options in the PROBPLOT statement to

specify or estimate shape parameters for the theoretical distribution
display a reference line corresponding to specified or estimated location and scale parameters for the theoretical distribution
request graphical enhancements

Note: Probability plots are similar to Q-Q plots, which you can create with the QQPLOT statement (see Chapter 10, "QQPLOT Statement"). Probability plots are preferable for graphical estimation of percentiles, whereas Q-Q plots are preferable for graphical estimation of distribution parameters and capability indices.

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