poisson.test {stats}  R Documentation 
Performs an exact test of a simple null hypothesis about the rate parameter in Poisson distribution, or for the ratio between two rate parameters.
poisson.test(x, T = 1, r = 1, alternative = c("two.sided", "less", "greater"), conf.level = 0.95)
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. 
Confidence intervals are computed similarly to those of
binom.test
in the onesample case, and using
binom.test
in the two sample case.
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 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,

alternative 
a character string describing the alternative hypothesis. 
method 
the character string 
data.name 
a character string giving the names of the data. 
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.
### 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))