The CDFPLOT statement plots the observed cumulative distribution function (cdf) of a variable, defined as

where is the number of nonmissing observations. The cdf is an increasing step function that has a vertical jump of at each value of equal to an observed value. The cdf is also referred to as the empirical cumulative distribution function (ecdf).

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

• superimpose specification limits

• superimpose fitted theoretical distributions (beta, exponential, gamma, lognormal, normal, and Weibull)

• specify graphical enhancements (such as color or text height)

You can also create a comparative cdf plot by using the CDFPLOT statement in conjunction with a CLASS statement.

You have three alternatives for producing cdf plots with the CDFPLOT statement:

• Traditional graphics are produced by default.

• ODS Graphics output is produced when you specify the ODS GRAPHICS statement prior to the PROC CAPABILITY statement.

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

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