PROC SHEWHART: Applying Tests to Range and Standard Deviation Charts

Applying Tests to Range and Standard Deviation Charts

[See SHWTSC3 in the SAS/QC Sample Library]If you are using the MRCHART, RCHART, SCHART, XRCHART, or XSCHART statement, you can use the TESTS2= option to request tests for special causes with an $\text{[math]}$ chart or $\text{[math]}$ chart. The syntax and test definitions for the TESTS2= option are identical to those for the TESTS= option, and you can use the ZONES2 and ZONE2LABELS options to display the zones on the secondary chart.

The following statements request Test 1 for a range chart of the data in Assembly (see Requesting Standard Tests):

ods graphics off;
title 'Analysis of Offset Ranges';
proc shewhart history=Assembly;
   rchart Offset * Sample / sigma0    = 2.24
                            limitn    = 5
                            alln
                            tests2    = 1
                            testlabel = (comment) ;
   label OffsetR = 'Offset Range in cm';
run;

The $\text{[math]}$ chart is shown in Figure 15.188.

Figure 15.188 Range Chart with Test 1

Caution: Except for requesting Test 1, use of the TESTS2= option is not recommended for general process control work. At the time of this writing, there is insufficient published research supporting the application of the other tests to $\text{[math]}$ charts and $\text{[math]}$ charts. There are no established guidelines for interpreting the other tests, nor are there assessments of their false signal probabilities or average run length characteristics. The TESTS2= option is intended primarily as a research tool.