The test results indicate points that are beyond the control limits. A failed point indicates that a nonrandom pattern exists in the data that may be the result of special-cause variation. You should investigate these points.

·    When a point fails a test, Minitab reports it in the Session window and marks it on the Generalized Variance chart. A failed point indicates that there is a nonrandom pattern in the data that may be the result of special-cause variation. These points should be investigated.

·    When no points are displayed under the test results, no points failed the tests for special causes.

For the plastics data, the test results indicate that subgroup 6 falls outside of the control limits. Investigate why this point is out of control.