** ^HELP ON EXACT POISSON PROBABILITY CALCULATION
      ^Joseph Hilbe - Stata Technical Bulletin  *** May 1991

The epoisson.ado file acts similar to a function in that a single answer
results. The call is...

   ^epoisson ^<^population ratio^>^ ^<^total observations^>^ ^<^cases^>

As an example, suppose that you know the overall 1990 hospital mortality
ratio for the state of Arizona, ie. the total number of deaths divided
by the total number of admissions. The value is .03 or 3% (it isn't!).
Now you wish to determine the exact poisson probability for the 20 deaths
which occurred in 1990 at St. Nowhere Hospital in Elsewhere, AZ. It's
total admissions for the year are 845. Type...

     ^epoisson .03 845 20^        the result shows...
     ^Exact poisson probability => .04831361	

which is a (.05) significant departure from what we might expect.