The Inability Of $\bar { X }$ Charts with 3-Sigma Limits to Quickly Detect Small Shifts in Limits

Multiple Choice

The inability of $\bar { X }$ charts with 3-sigma limits to quickly detect small shifts in the process mean has prompted investigators to develop procedures that provide improved behavior in this respect. Which of the following conditions need to be satisfied for an appropriated intervention to take corrective action?

A) Two out of three successive points fall outside 2-sigma limits on the same side of the center line.
B) Four out of five successive points fall outside 1-sigma limits on the same side of the center line.
C) Eight successive points fall on the same side of the center line.
D) All of the above.
E) None of the above.