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.

Question

Quizplus · Accepted Answer

These conditions are known as Western Electric rules or sometimes as the "two out of three", "four out of five", and "eight in a row" rules. They are used to detect smaller shifts in the process mean that might not be immediately obvious with just 3-sigma limits.

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

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