\Header{t.test}{Student's t-Test}
\keyword{htest}{t.test}
\begin{Description}\relax
t.test performs one and two sample t-tests on vectors of data.\end{Description}
\begin{Usage}
\begin{verbatim}
t.test(x, y = NULL, alternative = c("two.sided", "less", "greater"),
       mu = 0, paired = FALSE, var.equal = FALSE, conf.level = 0.95)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] a numeric vector of data values.
\item[\code{y}] an optional numeric vector data values.
\item[\code{alternative}] character specifying the alternative hypothesis,
must be one of \code{"two.sided"} (default), \code{"greater"} or
\code{"less"}.  You can specify just the initial letter.
\item[\code{mu}] a number indicating the true value of the mean (or
difference in means if you are performing a two sample test).
\item[\code{paired}] a logical indicating whether you want a paired
t-test.
\item[\code{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[\code{conf.level}] confidence level of the interval.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
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.  By default, 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.\end{Details}
\begin{Value}
A list with class \code{"htest"} containing the following
components:
\begin{ldescription}
\item[\code{statistic}] the value of the t-statistic.
\item[\code{parameters}] the degrees of freedom for the t-statistic.
\item[\code{p.value}] the p-value for the test.
\item[\code{conf.int}] a confidence interval for the mean appropriate to
the specified alternative hypothesis.
\item[\code{estimate}] the estimated mean or difference in means depending
on whether it was a one-sample test or a two-sample test.
\item[\code{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[\code{alternative}] a character string describing the alternative
hypothesis.
\item[\code{method}] a character string indicating what type of t-test was
performed.
\item[\code{data.name}] a character string giving the name(s) of the data.
\end{ldescription}
\end{Value}
\begin{Examples}
\begin{ExampleCode}
t.test(1:10,y=c(7:20))      # P = .00001855
t.test(1:10,y=c(7:20, 200)) # P = .1245    -- NOT significant anymore
\end{ExampleCode}
\end{Examples}

