COMPHISTOGRAM Statement: CAPABILITY Procedure
Comparative histograms are useful for comparing the distribution of a process variable across levels of classification variables. You can use the COMPHISTOGRAM statement to create one-way and two-way comparative histograms. When used with a single classification variable, the COMPHISTOGRAM statement displays an array of component histograms (stacked or side-by-side), one for each level of the classification variable. When used with two classification variables, the COMPHISTOGRAM statement displays a matrix of component histograms, one for each combination of levels of the classification variables.
In quality improvement applications, typical uses of comparative histograms include
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comparing the capability of a process before and after an improvement
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comparing process capabilities of two or more suppliers
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exploring stratification in process data due to different lots, machines, manufacturing methods, and so forth
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studying the evolution of process capability over successive time periods
You can use options in the COMPHISTOGRAM statement to
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specify the midpoints or endpoints for histogram intervals
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specify the number of rows and/or columns of component histograms
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display specification limits on the component histograms
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display density curves for fitted normal distributions
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display kernel density estimates
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request graphical enhancements
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inset summary statistics and process capability indices on the component histograms
You have two alternatives for producing comparative histograms with the COMPHISTOGRAM statement:
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ODS Graphics output is produced if ODS Graphics is enabled, for example by specifying the ODS GRAPHICS ON statement prior to the PROC statement.
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Otherwise, traditional graphics are produced if SAS/GRAPH® is licensed.
See Chapter 3: SAS/QC Graphics, for more information about producing these different kinds of graphs.
Note: You cannot use the COMPHISTOGRAM statement together with the CLASS statement.