Statistical Process Control charts are used to detect whether a ...

[Themember4]

Statistical Process Control charts are used to detect whether a process remains in control or whether it has gone out of control. Explain how the SPC signals work.
 
  What will be an ideal response?

Question 2

Which of the following is true regarding the MSE and MAD in forecasting?
 
  A) The MAD will tend to be a larger value than the MSE.
  B) The MSE is much more useful than the MAD.
  C) The square root of the MSE provides a value that will be similar to the MAD.
  D) The MAD will be equal to the MSE.

[EAN94]

Answer to Question 1

The control limits on an SPC chart are typically set at the 3-sigma level. This means that if the process remains unchanged, approximately 99.7 percent of the observations will fall within the control limits. Thus, under normal circumstances it would be most unusual for a measurement to fall outside the upper or lower control limits if nothing has changed. The signals that something has changed are:
1. one or more points outside the control limits
2. nine or more points in a row above or below the center line
3. six or more points moving in the same direction (up or down).
These limits are all set such that the probability of one of these events happening if the process is actually unchanged (in control) is very small. Therefore, if such an event exists, we should conclude that something has changed and the process is out of control. These rules guard against the Type I errorsaying the process is out of control when it isn't.

Answer to Question 2

C