The SHEWHART Procedure

Applying Tests to Range and Standard Deviation Charts

Note: See Applying Tests for Special Causes-R charts 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 R chart or s 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 R chart is shown in Figure 17.187.

Figure 17.187: 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 R charts and s 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.