These functions calculate confidence intervals for a Poisson count or
rate using an exact method (pois.exact
), gamma distribution
(pois.daly
), Byar's formula (pois.byar
), or normal
approximation to the Poisson distribution (pois.approx
).
To calculate an exact confidence interval for a crude rate (count
divided by person-time at risk), set pt
equal to the
person-time at risk. Both x
and pt
can be either a
number or a vector of numbers.
The pois.daly
function gives essentially identical answers to
the pois.exact
function except when x = 0. When x = 0, for the
upper confidence limit pois.exact
returns 3.689 and
pois.daly
returns 2.996.