The R Project SVN R

\name{prop.test}
\title{Test for Equal or Given Proportions}
\usage{
prop.test(x, n, p = NULL, alternative = "two.sided",
          conf.level = 0.95, correct = TRUE)
}
\alias{prop.test}
\arguments{
  \item{x, n}{vectors of counts of successes and trials, respectively.
    Only pairs with finite values are used.  The elements of \code{x}
    must be nonnegative and not greater than the corresponding elements
    of \code{n} which must be positive.  All elements should be
    integers.}
  \item{p}{a vector of probabilities of success.  \code{p} must have the
    same length as \code{x} and \code{n}, and its elements must be
    greater than 0 and less than 1.}
  \item{alternative}{indicates the alternative hypothesis and must be
    one of \code{"two.sided"}, \code{"greater"} or \code{"less"}.  You
    can specify just the initial letter.  Only used for testing the null
    that a single proportion equals a given value, or that two
    proportions are equal;  ignored otherwise.}
  \item{conf.level}{confidence level of the returned confidence
    interval.  Must be a single number between 0 and 1.  Only used when
    testing the null that a single proportion equals a given value, or
    that two proportions are equal;  ignored otherwise.}
  \item{correct}{a logical indicating whether Yates' continuity
    correction should be applied.}
}
\description{
  \code{prop.test} can be used for testing the null that the proportions
  (probabilities of success) in several groups are the same, or that
  they equal certain given values.

  If \code{p} is \code{NULL} and there is more than one group, the null
  tested is that the proportions in each group are the same.  If there
  are two groups, the alternatives are that the probability of success
  in the first group is less than, not equal to, or greater than the
  probability of success in the second group, as specified by
  \code{alternative}.  A confidence interval for the difference of
  proportions with confidence level as specified by \code{conf.level}
  and clipped to \eqn{[-1,1]} is returned.  Continuity correction is
  used only if it does not exceed the difference of the sample
  proportions in absolute value.  Otherwise, if there are more than 2
  groups, the alternative is always \code{"two.sided"}, the returned
  confidence interval is \code{NULL}, and continuity correction is never
  used.

  If there is only one group, then the null tested is that the
  underlying probability of success is \code{p}, or .5 if \code{p} is
  not given.  The alternative is that the probability of success if less
  than, not equal to, or greater than \code{p} or 0.5, respectively, as
  specified by \code{alternative}.  A confidence interval for the
  underlying proportion with confidence level as specified by
  \code{conf.level} and clipped to \eqn{[0,1]} is returned.  Continuity
  correction is used only if it does not exceed the difference between
  sample and null proportions in absolute value.

  Finally, if \code{p} is given and there are more than 2 groups, the
  null tested is that the underlying probabilities of success are those
  given by \code{p}.  The alternative is always \code{"two.sided"}, the
  returned confidence interval is \code{NULL}, and continuity correction
  is never used.
}
\value{
  A list with class \code{"htest"} containing the following components:
  \item{statistic}{the value of Pearson's chi-square test statistic.}
  \item{parameter}{the degrees of freedom of the approximate chi-square
    distribution of the test statistic.}
  \item{p.value}{the p-value of the test.}
  \item{estimate}{a vector with the sample proportions \code{x/n}.}
  \item{conf.int}{a confidence interval for the true proportion if there
    is one group, or for the difference in proportions if there are 2
    groups and \code{p} is not given, or \code{NULL} otherwise.  In the
    cases where it is not \code{NULL}, the returned confidence interval
    has an asymptotic confidence level as specified by
    \code{conf.level}, and is appropriate to the specified alternative
    hypothesis.}
  \item{null.value}{the value of \code{p} if specified by the null, or
    \code{NULL} otherwise.}
  \item{alternative}{a character string describing the alternative.}
  \item{method}{a character string indicating the method used, and
    whether Yates' continuity correction was applied.}
  \item{data.name}{a character string giving the names of the data.}
}
\keyword{htest}