Applying Tests to Range and Standard Deviation Charts

Tests for Special Causes

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 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" ):

   symbol v=dot c=salmon;
   title 'Analysis of Offset Ranges';
   proc shewhart history=assembly;
      rchart offset * sample / sigma0    = 2.24
                               limitn    = 5
                               alln
                               tests2    = 1
                               testlabel = (comment) 
                               cframe    = vligb
                               cinfill   = ywh
                               cconnect  = salmon
                               ctests    = black;
      label offsetr = 'Offset Range in cm';
   run;

The R chart is shown in Figure 48.10.

Figure 48.10: 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.

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