It is impossible for the X-bar chart to be out of control without the range chart also being out of control.

Question

Quizplus · Accepted Answer

It is possible for the X-bar chart to be out of control without the range chart being out of control if the process has a stable range but an unstable mean. Conversely, it is also possible for the range chart to be out of control without the X-bar chart being out of control if there is a sudden increase or decrease in process variability without a corresponding shift in the process mean.

It Is Impossible for the X-Bar Chart to Be Out