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XCHART Statement |
See SHWTEST in the SAS/QC Sample Library |
This example illustrates how you can apply tests for special causes to make charts more sensitive to special causes of variation.
The following statements create an chart for the gap width measurements in the data set PARTS at "Creating Charts for Means from Subgroup Summary Data" and tabulate the results:
title 'Tests for Special Causes Applied to Gap Width Data'; symbol v=dot c=yellow; proc shewhart history=parts; xchart partgap*sample/ tests = 1 to 5 ltests = 20 tabletests tablecentral tablelegend zonelabels nolegend cframe = vigb cinfill = vlib ctests = red cconnect = yellow; run;The chart is shown in Output 42.1.1 and the printed output is shown in Output 42.1.2. The TESTS= requests Tests 1, 2, 3, 4, and 5, which are described in Chapter 48, "Tests for Special Causes." The TABLECENTRAL option requests a table of the subgroup means, control limits, and central line. The TABLETESTS option adds a column indicating which subgroups tested positive for special causes, and the TABLELEGEND option adds a legend describing the tests that were signaled.
The ZONELABELS option displays zone lines and zone labels on the chart. The zones are used to define the tests. The LTESTS= option specifies the line type used to connect the points in test patterns that were signaled. The NOLEGEND option suppresses the subgroup sample size legend that is displayed by default in the lower left corner of the chart.
Output 42.1.1 and Output 42.1.2 indicate that Test 5 was positive at sample 14, signaling a possible shift in the mean of the process.
Output 42.1.1: Tests for Special Causes Displayed on an Chart
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