Minitab conducts up to four tests for special causes for the P chart, which detect points beyond the control limits and specific patterns in the data. When a data point fails a test, Minitab reports it in the Session window and marks the point on the P chart. A failed point indicates that there is an unusual value or a nonrandom pattern, either of which may be the result of special-cause variation. These points should be investigated.

No points failed the tests for special causes.

The telephone data did not fail any of the tests for special causes. Therefore, the P chart is in control.