Example 2.2: Using Reference Lines with CDF Plots

CDFPLOT Statement

Example 2.2: Using Reference Lines with CDF Plots

See CAPCDF1 in the SAS/QC Sample Library

Customer requirements dictate that the breaking strengths in the previous example have upper and lower specification limits of 7.2 and 6.8 psi, respectively. Moreover, less than 5% of the cords can have breaking strengths outside the limits.

The following statements create a cdf plot with reference lines at the 5% and 95% cumulative percent levels:

   title 'Cumulative Distribution Function of Breaking Strength';
   legend1 frame cframe=ligr cborder=black position=center;
   proc capability data=cord noprint;
      spec lsl=6.8 llsl=2 usl=7.2 lusl=2 cusl=red clsl=blue;
      cdf strength /  vref         = 5 95
                      vreflabels   = '5%' '95%'
                      vaxis        = axis1
                      cframe       = ligr
                      cvref        = black
                      legend       = legend1;
      inset pctgtr pctlss / cfill  = blank
                            format = 5.2
                            pos    = e
                            header = "Summary Statistics";
      axis1 label=(a=90 r=0);
   run;

The INSET statement requests an inset with the percentages of measurements above the upper limit and below the lower limit. For more information about the INSET statement, see Chapter 5, "INSET Statement" .

In Output 2.2.1, the empirical cdf is below the intersection between the lower specification limit line and the 5% line, so less than 5% of the measurements are below the lower limit. The ecdf, however, is also below the intersection between the upper specification limit line and the 95% line, implying that more than 5% of the measurements are greater than the upper limit. Thus, the goal of having less than 5% of the measurements above the upper specification limit has not been met.

Output 2.2.1: Reference Lines with a Cumulative Distribution Function Plot

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