Modified Shewhart-exponentially weighted moving average control charts

A modified Shewhart-exponentially weighted moving average X-bar statistical control scheme is evaluated. It is characterized by the use of a Shewhart component requiring two (or more) plotted points beyond reduced width (i.e., less than three-sigma) control limits to give an out-of-control signal. Schemes with both better average run length profiles and better early false-signal characteristics than those associated with standard Shewhart-runs rules schemes are suggested.