Investigate any subgroups that fail the tests for special causes. By default, Minitab conducts only Test 1, which detects points that fall outside of the control limits. However, if you conduct additional tests, then points can fail multiple tests. The Session window output shows exactly which points failed each test, as shown here.
TEST 1. One point more than 3.00 standard deviations from center line.
Test Failed at points: 8
* WARNING * If graph is updated with new data, the results above may no longer
When you use several tests at the same time, the sensitivity of the chart increases. However, the false alarm rate also increases, which can make you react to the test results unnecessarily.
For more information on each of the tests and when to use them, go to Using tests for special causes in control charts.