Definition of Rare Event SPC:
Some events occur so rarely that we can not use the traditional control charts like I-Mr, Xbar-R or P charts, to monitor. Instead we use so called rare event control charts, that show the amount of time or the number of opportunities between these events.
There are two types of rare event charts:
- T-chart measures the time elapsed since the last event and
- G-chart counts the number of possible opportunities since the last even