poisson.test
Exact Poisson tests
Performs an exact test of a simple null hypothesis about the rate parameter in Poisson distribution, or for the ratio between two rate parameters.
 Keywords
 htest
Usage
poisson.test(x, T = 1, r = 1, alternative = c("two.sided", "less", "greater"), conf.level = 0.95)
Arguments
 x
 number of events. A vector of length one or two.
 T
 time base for event count. A vector of length one or two.
 r
 hypothesized rate or rate ratio
 alternative
 indicates the alternative hypothesis and must be
one of
"two.sided"
,"greater"
or"less"
. You can specify just the initial letter.  conf.level
 confidence level for the returned confidence interval.
Details
Confidence intervals are computed similarly to those of
binom.test
in the onesample case, and using
binom.test
in the two sample case.
Value

A list with class
 statistic
 the number of events (in the first sample if there are two.)
 parameter
 the corresponding expected count
 p.value
 the pvalue of the test.
 conf.int
 a confidence interval for the rate or rate ratio.
 estimate
 the estimated rate or rate ratio.
 null.value
 the rate or rate ratio under the null,
r
.  alternative
 a character string describing the alternative hypothesis.
 method
 the character string
"Exact Poisson test"
or"Comparison of Poisson rates"
as appropriate.  data.name
 a character string giving the names of the data.
"htest"
containing the following components:
Note
The rate parameter in Poisson data is often given based on a
“time on test” or similar quantity (personyears, population
size, or expected number of cases from mortality tables). This is the
role of the T
argument.
The onesample case is effectively the binomial test with a very large
n
. The two sample case is converted to a binomial test by
conditioning on the total event count, and the rate ratio is directly
related to the odds in that binomial distribution.
See Also
Examples
library(stats)
### These are paraphrased from data sets in the ISwR package
## SMR, Welsh Nickel workers
poisson.test(137, 24.19893)
## eba1977, compare Fredericia to other three cities for ages 5559
poisson.test(c(11, 6+8+7), c(800, 1083+1050+878))