PK0-003 · Question #355
Upper and lower control limits could be set at a standard deviation of three. Which of the following represents the associated confidence level?
The correct answer is C. 99.7%. Setting upper and lower control limits at three standard deviations from the mean corresponds to a confidence level of 99.7%, a key principle in statistical quality control.
Question
Upper and lower control limits could be set at a standard deviation of three. Which of the following represents the associated confidence level?
Options
- A68%
- B95%
- C99.7%
- D99.999%
How the community answered
(21 responses)- A5% (1)
- B5% (1)
- C90% (19)
Why each option
Setting upper and lower control limits at three standard deviations from the mean corresponds to a confidence level of 99.7%, a key principle in statistical quality control.
A confidence level of 68% is associated with data falling within one standard deviation from the mean in a normal distribution.
A confidence level of 95% is associated with data falling within two standard deviations from the mean in a normal distribution.
According to the empirical rule (or 68-95-99.7 rule) for a normal distribution, approximately 99.7% of all data points fall within three standard deviations (plus or minus) from the mean. Therefore, control limits set at plus or minus three standard deviations encompass 99.7% of the expected variations, making it the associated confidence level.
A confidence level of 99.999% is associated with data falling within 4.5 standard deviations from the mean in a normal distribution, not three standard deviations.
Concept tested: Statistical process control-Empirical Rule
Topics
Community Discussion
No community discussion yet for this question.