While performing monthly reviews, in the control chart of one of your production unit, you observe that the last 50 points are very near to the center line. All of them appear to be within about one sigma of the center line. What Interpretation would you derive from this?

OPTIONS

• Somebody miscalculated the original calculations of the control limits
• The process standard deviation has decreased during last month and hence the last 50 data points are showing values much closer to the center line, But, nobody thought to recompute the control limits to reflect the new reality
• This is an out of control situation. Get a team in place right away and see what the trouble is.
• The process is in control. The closer the points are to the center line the better control of the process is. No action is needed, process and the control limits to continue as it is

ANSWER

This is an out of control situation. Get a team in place right away and see what the trouble is.

EXPLANATION

FIRST OPTION is obviously incorrect, the control limits would have been set up correctly in the first place. THIRD OPTION is incorrect, the process is not out of control. FOURTH OPTIONS is partially correct because as the process improves, we need to fix the limits as well. So THIRD OPTION is the correct answer.