Question

Choose the best answer. Which of the following signals should be considered out of control on control charts?

A point outside the 3? control limits AND nine consecutive points above the center line or nine consecutive points below the center line on the ?¯chart AND nine points either above or below the center line on the ?¯chart are considered out of control on control charts.

Nine consecutive points above the center line or nine consecutive points below the center line on the ?¯ chart is considered out of control on control charts.

A point outside the 3? control limits is considered out of control on control charts.

Nine points either above or below the center line on the ?¯ chart is considered out of control on control charts.

A point outside the 3? control limits AND nine consecutive points above the center line or nine consecutive points below the center line on the ?¯ chart are considered out of control on control charts.

Answer 1

option D is correct answer

because we know that the process is out of control only when the points fall outside 3 sigma and 9 consecutive points are either below or above the center line. So, option D met conditions

option A is incorrect because we need consecutive 9 points, but not any 9 points below or above the center line. So, one condition is not satisfied

option B is incorrect because it only shows one condition, but not showing the condition fo 3 sigma. So, it is incomplete

option C is incorrect because we need consecutive 9 points, but not any 9 points below or above the center line. So, one condition is not satisfied