The CAPABILITY Procedure


Overview: PPPLOT Statement

The PPPLOT statement creates a probability-probability plot (also referred to as a P-P plot or percent plot), which compares the empirical cumulative distribution function (ecdf) of a variable with a specified theoretical cumulative distribution function such as the normal. If the two distributions match, the points on the plot form a linear pattern that passes through the origin and has unit slope. Thus, you can use a P-P plot to determine how well a theoretical distribution models a set of measurements.

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

  • beta

  • exponential

  • gamma

  • Gumbel

  • inverse Gaussian

  • lognormal

  • normal

  • generalized Pareto

  • power function

  • Rayleigh

  • Weibull

You can use options in the PPPLOT statement to do the following:

  • specify or estimate parameters for the theoretical distribution

  • request graphical enhancements

You can also create a comparative P-P plot by using the PPPLOT statement in conjunction with a CLASS statement.

You have three alternatives for producing P-P plots with the PPPLOT statement:

  • ODS Graphics output is produced if ODS Graphics is enabled, for example by specifying the ODS GRAPHICS ON statement prior to the PROC statement.

  • Otherwise, traditional graphics are produced by default if SAS/GRAPHĀ® is licensed.

  • Legacy line printer charts are produced when you specify the LINEPRINTER option in the PROC statement.

See ChapterĀ 3: SAS/QC Graphics, for more information about producing these different kinds of graphs.

Note: Probability-probability plots should not be confused with probability plots, which compare a set of ordered measurements with percentiles from a specified distribution. You can create probability plots with the PROBPLOT statement.