Upper and lower control limits are usually based upon _______.
A)± 3 standard deviations
B)± 2 standard deviations
C)± 1 standard deviation
D)± 4 standard deviations
E)± 6 standard deviations

Question

Quizplus · Accepted Answer

Upper and lower control limits are typically set at ± 3 standard deviations from the process mean in statistical quality control. This is because ± 3 standard deviations encompass about 99.73% of the data assuming a normal distribution, providing a balance between sensitivity to process shifts and the rate of false alarms.

Upper and Lower Control Limits Are Usually Based Upon _______