The formulas for determining the upper and lower control limits are based on the number of standard deviations, z, from the process average. Management usually selects a z value of _______because it wants a high probability that these sample values will fall within the control limits.
A) one
B) two
C) three
D) six

Question

Quizplus · Accepted Answer

Management usually selects a z value of three because it provides a high level of confidence (99.73%) that the process is within control limits. A z value of one or two would provide lower levels of confidence, while a z value of six would be overly stringent and result in a high number of false positives.

The Formulas for Determining the Upper and Lower Control Limits