You are developing an X-bar chart based on sample means. You know the standard deviation of the sample means is 4, the desired confidence level is 99.7 percent, and the average of the sample means is 24. Which of the following is your UCL?
A) 36
B) 24
C) 12
D) 4
E) None of these choices are correct.

Question

Quizplus · Accepted Answer

The UCL (Upper Control Limit) for an X-bar chart is calculated as the average of the sample means plus the product of the standard deviation of the sample means and the Z-score for the desired confidence level. For 99.7% confidence, the Z-score is 3. Therefore, UCL = 24 + (3 * 4) = 36.

You Are Developing an X-Bar Chart Based on Sample Means