The lower and upper control limits of an control chart are usually set at:
A)± one standard error from the centerline.
B)± two standard errors from the centerline.
C)± three standard errors from the centerline.
D)None of these choices.

Question

The lower and upper control limits of an  control chart are usually set at:
A)± one standard error from the centerline. 
B)± two standard errors from the centerline. 
C)± three standard errors from the centerline. 
D)None of these choices.

Quizplus · Accepted Answer

The lower and upper control limits of the 11ea78b9_2e5d_7173_8379_538fa50ab270_TB4388_11 control chart are usually set at ± three standard errors from the centerline. This criterion ensures that the control limits are at a sufficient distance from the central line, so that only statistically significant variation in the process is identified as out of control. Setting the control limits at one or two standard errors from the centerline may cause too many false alarms or not detect significant shifts in the process. Therefore, C is the best choice.

The Lower and Upper Control Limits of an Control