ASQ Certified Quality Engineer (CQE) — Question 82

An X-bar chart has shown control for a long time. You see that points for the last 50 samples are all very near the center line on the chart. In fact, they are all within one sigma of the center line. This probably indicates that

Answer options

• A. It is a desirable situation.
• B. It is an undesirable situation.
• C. The process standard deviation has decreased during the time the last 50 samples were taken.
• D. The control charts are incorrectly computed.

Correct answer: C

Explanation

The correct answer, C, suggests that the points being close to the center line and within one sigma indicates improved process stability, which typically implies a decrease in process variation. Options A and B are subjective and do not directly explain the statistical behavior observed. Option D is incorrect because the X-bar chart has shown control, indicating that the calculations are likely accurate.