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 |
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))
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Licensed under the GNU General Public License.