A simple, easy-to-use graphical method is presented for use in determining if
there is any statistically significant trend or pattern over time in an underlying
Poisson event rate of occurrence or binomial failure on demand probability.
The method is based on the combined use of both an exponentially weighted
moving-average (EWMA) and a Shewhart chart. Two nuclear power plant
examples are introduced and used to illustrate the method. The false alarm
probability and power when using the combined procedure are also determined
for both cases using Monte Carlo simulation. The results indicate that
the combined procedure is quite effective in rapidly detecting either a small or
large step increase in the Poisson rate or binomial probability over time.