A single chart for monitoring frequency and magnitude of events

This article presents a single Statistical Process Control (SPC) chart for simultaneously monitoring the time interval T and magnitude X of an event. The new chart is called a G chart as it deals with a synthetic statistic G. The G chart makes use of the information about the event frequency as well as the information about the event magnitude. Moreover, its detection power can be allocated in an optimal manner between that against T shifts and that against X shifts, and between that against small shifts and that against large shifts. As a result, the G chart is more effective than all other charts currently available in the literature for detecting the out-of-control status of an event. Moreover, comparing with other charts, the G chart performs more uniformly for detecting process shifts of different types and sizes.