The moving range (MR) chart assesses whether the process variation is in control. The tests for special causes detect points beyond the control limits and specific patterns in the data.

·    When an observation fails a test, Minitab reports it in the Session window and marks it on the MR 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 observations failed the tests for special causes.

No points failed the tests for special causes.

The liquid detergent data did not fail any of the tests for special causes. Therefore, the process variation is in control.