Example 1.2: Labeling Histogram Endpoints

The CAPABILITY Procedure

Example 1.2: Labeling Histogram Endpoints

This example uses the trans data set from the preceding example.

By default, major tick marks on the horizontal axis of a histogram correspond to midpoints of the histogram intervals (see Output 1.1.1). You can use the ENDPOINTS= and NENDPOINTS= options to create histograms and comparative histograms whose interval boundaries, or endpoints, are aligned with major tick marks. The following statements create the histogram shown in Output 1.2.1:

   title 'Process Capability Analysis of Plating Thickness';
   proc capability data=trans noprint;
      spec lsl = 3.45 llsl = 2 clsl = black
           usl = 3.55 lusl = 2 cusl = black;
      histogram thick / cframe = ligr
                        cfill  = blue
                        endpoints;
   run;

Output 1.2.1: Histogram with Endpoints Labeled

The tick mark values in Output 1.2.1 are identical to those in Output 1.1.1, but the histogram intervals lie between the tick marks. Because their intervals have different boundaries, the histograms in Output 1.1.1 and Output 1.2.1 look somewhat different. Note that a histogram produced with the ENDPOINTS option will not necessarily have the same tick mark values on its horizontal axis as a histogram of the same data produced without the ENDPOINTS option.

You can use the NMIDPOINTS= or the NENDPOINTS= option to specify the number of interval midpoints or endpoints in a histogram. The following statements create the histogram shown in Output 1.2.2:

   title 'Process Capability Analysis of Plating Thickness';
   proc capability data=trans noprint;
      spec lsl = 3.45 llsl = 2 clsl = black
           usl = 3.55 lusl = 2 cusl = black;
      histogram thick / cframe     = ligr
                        cfill      = blue
                        nendpoints = 13;
   run;

Output 1.2.2: Histogram with Number of Endpoints Specified

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