| poisson.test {stats} | R Documentation |
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 |
conf.level |
confidence level for the returned confidence interval. |
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.
Value
A list with class "htest" containing the following components:
statistic |
the number of events (in the first sample if there are two.) |
parameter |
the corresponding expected count |
p.value |
the p-value 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,
|
alternative |
a character string describing the alternative hypothesis. |
method |
the character string |
data.name |
a character string giving the names of the data. |
Note
The rate parameter in Poisson data is often given based on a
“time on test” or similar quantity (person-years, population
size, or expected number of cases from mortality tables). This is the
role of the T argument.
The one-sample 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
### 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))