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<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><title>R: Exact Poisson tests</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> <link rel="stylesheet" type="text/css" href="R.css" /> </head><body> <table width="100%" summary="page for poisson.test {stats}"><tr><td>poisson.test {stats}</td><td style="text-align: right;">R Documentation</td></tr></table> <h2>Exact Poisson tests</h2> <h3>Description</h3> <p>Performs an exact test of a simple null hypothesis about the rate parameter in Poisson distribution, or for the ratio between two rate parameters. </p> <h3>Usage</h3> <pre> poisson.test(x, T = 1, r = 1, alternative = c("two.sided", "less", "greater"), conf.level = 0.95) </pre> <h3>Arguments</h3> <table summary="R argblock"> <tr valign="top"><td><code>x</code></td> <td> <p>number of events. A vector of length one or two.</p> </td></tr> <tr valign="top"><td><code>T</code></td> <td> <p>time base for event count. A vector of length one or two. </p> </td></tr> <tr valign="top"><td><code>r</code></td> <td> <p>hypothesized rate or rate ratio</p> </td></tr> <tr valign="top"><td><code>alternative</code></td> <td> <p>indicates the alternative hypothesis and must be one of <code>"two.sided"</code>, <code>"greater"</code> or <code>"less"</code>. You can specify just the initial letter.</p> </td></tr> <tr valign="top"><td><code>conf.level</code></td> <td> <p>confidence level for the returned confidence interval.</p> </td></tr> </table> <h3>Details</h3> <p>Confidence intervals are computed similarly to those of <code><a href="binom.test.html">binom.test</a></code> in the one-sample case, and using <code><a href="binom.test.html">binom.test</a></code> in the two sample case. </p> <h3>Value</h3> <p>A list with class <code>"htest"</code> containing the following components: </p> <table summary="R valueblock"> <tr valign="top"><td><code>statistic</code></td> <td> <p>the number of events (in the first sample if there are two.)</p> </td></tr> <tr valign="top"><td><code>parameter</code></td> <td> <p>the corresponding expected count</p> </td></tr> <tr valign="top"><td><code>p.value</code></td> <td> <p>the p-value of the test.</p> </td></tr> <tr valign="top"><td><code>conf.int</code></td> <td> <p>a confidence interval for the rate or rate ratio.</p> </td></tr> <tr valign="top"><td><code>estimate</code></td> <td> <p>the estimated rate or rate ratio.</p> </td></tr> <tr valign="top"><td><code>null.value</code></td> <td> <p>the rate or rate ratio under the null, <code>r</code>.</p> </td></tr> <tr valign="top"><td><code>alternative</code></td> <td> <p>a character string describing the alternative hypothesis.</p> </td></tr> <tr valign="top"><td><code>method</code></td> <td> <p>the character string <code>"Exact Poisson test"</code> or <code>"Comparison of Poisson rates"</code> as appropriate.</p> </td></tr> <tr valign="top"><td><code>data.name</code></td> <td> <p>a character string giving the names of the data.</p> </td></tr> </table> <h3>Note</h3> <p>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 <code>T</code> argument. </p> <p>The one-sample case is effectively the binomial test with a very large <code>n</code>. 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. </p> <h3>See Also</h3> <p><code><a href="binom.test.html">binom.test</a></code> </p> <h3>Examples</h3> <pre> ### 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)) </pre> <hr /><div style="text-align: center;">[Package <em>stats</em> version 3.6.0 <a href="00Index.html">Index</a>]</div> </body></html>