Consider the purity data in Exercise
Use
and assume that the desired process target is 90 .
(a) Construct an EWMA control chart with
. Does the process appear to be in control?
(b) Construct an EWMA control chart with
. Compare your results to part (a).
(c) Suppose that the next five observations are 90.75,90.00 ,
and
Apply the EWMAs in part (a) and
(b) to these new observations. Is there any evidence that the process has shifted out of control?