Modifying Standard Tests for Special Causes

Tests for Special Causes

Modifying Standard Tests for Special Causes

Some textbooks and references present slightly different versions of Tests 2 and 3. You can use the following options to request these modifications:

TEST2RUN=run-length specifies the length of the pattern for Test 2. The form of the test for each run-length is given in the following table. The default run-length is 9.

Run-length Number of Points on One Side of Central Line

7 7 in a row

8 8 in a row

9 9 in a row

11 at least 10 out of 11 in a row

14 at least 12 out of 14 in a row

20 at least 16 out of 20 in a row

TEST3RUN=run-length specifies the length of the pattern for Test 3. The run-length values allowed are 6, 7, and 8. The default run-length is 6.

The Western Electric Company (now AT&T) Statistical Quality Control Handbook and Montgomery (1996) discuss a test that is signaled by eight points in a row in Zone C or beyond (on one side of the central line). You can request this test by specifying TESTS=2 and TEST2RUN=8. The Handbook also discusses tests corresponding to Tests 1, 5, 6, 7, and 8.

Kume (1985) recommends a number of tests for special causes that can be regarded as modifications of Tests 2 and 3:

seven points in a row on one side of the central line. Specify TESTS=2 and TEST2RUN=7.
at least 10 out of 11 points in a row on one side of the central line. Specify TESTS=2 and TEST2RUN=11.
at least 12 out of 14 points in a row on one side of the central line. Specify TESTS=2 and TEST2RUN=14.
at least 16 out of 20 points in a row on one side of the central line. Specify TESTS=2 and TEST2RUN=20.
seven points in a row steadily increasing or decreasing. Specify TESTS=3 and TEST3RUN=7.

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*Run-length*	Number of Points on One Side of Central Line
7	7 in a row
8	8 in a row
9	9 in a row
11	at least 10 out of 11 in a row
14	at least 12 out of 14 in a row
20	at least 16 out of 20 in a row