# poisson.test: Exact Poisson tests

## Description

Performs an exact test of a simple null hypothesis about the
rate parameter in Poisson distribution, or for the
ratio between two rate parameters.

## 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.

## Value

A list with class `"htest"`

containing the following components:

statisticthe number of events (in the first sample if there
are two.)

parameterthe corresponding expected count

p.valuethe p-value of the test.

conf.inta confidence interval for the rate or rate ratio.

estimatethe estimated rate or rate ratio.

null.valuethe rate or rate ratio under the null,
`r`

.

alternativea character string describing the alternative
hypothesis.

methodthe character string `"Exact Poisson test"`

or
`"Comparison of Poisson rates"`

as appropriate.

data.namea character string giving the names of the data.

## Details

Confidence intervals are computed similarly to those of
`binom.test`

in the one-sample case, and using
`binom.test`

in the two sample case.

## Examples

# NOT RUN {
### 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 55-59
poisson.test(c(11, 6+8+7), c(800, 1083+1050+878))
# }