The R Project SVN R

\name{t.test}
\alias{t.test}
\title{Student's t-Test}
\usage{
t.test(x, y = NULL, alternative = "two.sided", mu = 0, paired = FALSE,
       var.equal = FALSE, conf.level = 0.95)
}
\arguments{
    \item{x}{a numeric vector of data values.}
    \item{y}{an optional numeric vector data values.}
    \item{alternative}{must be one of \code{"two.sided"},
    \code{"greater"} or \code{"less"}.  You can specify just the
    initial letter.  This parameter indicates the alternative
    hypothesis.}
    \item{mu}{a number indicating the true value of the mean (or
    difference in means if you are performing a two sample test).}
    \item{paired}{a logical indicating whether you want a paired
    t-test.}
    \item{var.equal}{a logical variable indicating whether to treat the
    two variances as being equal. If \code{TRUE} then the pooled
    variance is used to estimate the variance otherwise the Welch
    approximation to the degrees of freedom is used.}
    \item{conf.level}{confidence level of the interval.}
}
\description{
    t.test performs one and two sample t-tests on vectors of data.
}
\details{
    If \code{paired} is \code{TRUE} then both \code{x} and \code{y} must
    be specified and they must be the same length.  Missing values are
    removed (in pairs if \code{paired} is \code{TRUE}).  If
    \code{var.equal} is \code{TRUE} then the pooled estimate of the
    variance is used. If \code{var.equal} is \code{FALSE} then the
    variance is estimated separately for both groups and the Welch
    modification to the degrees of freedom is used.
}
\value{
    A list with class \code{"htest"} containing the following
    components:
    \item{statistic}{the value of the t-statistic.}
    \item{parameters}{the degrees of freedom for the t-statistic.}
    \item{p.value}{the p-value for the test.}
    \item{conf.int}{a confidence interval for the mean appropriate to
    the specified alternative hypothesis.}
    \item{estimate}{the estimated mean or difference in means depending
    on whether it was a one-sample test or a two-sample test.}
    \item{null.value}{the specified hypothesized value of the mean or
    mean difference depending on whether it was a one-sample test or
    a two-sample test.}
    \item{alternative}{a character string describing the alternative
        hypothesis.}
    \item{method}{a character string indicating what type of t-test was
        performed.}
    \item{data.name}{a character string giving the name(s) of the data.}
}
\seealso{\code{\link{prop.test}}
\examples{
t.test(1:10,y=c(7:20))      # P = .00001855
t.test(1:10,y=c(7:20, 200)) # P = .1245    -- NOT significant anymore
}
\keyword{htest}