\Header{t.test}{Student's t-Test}
\keyword{htest}{t.test}
\begin{Usage}
\begin{verbatim}
t.test(x, y = NULL, alternative = "two.sided", mu = 0, paired = FALSE,
       var.equal = FALSE, conf.level = 0.95)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\texttt{x}] a numeric vector of data values.
\item[\texttt{y}] an optional numeric vector data values.
\item[\texttt{alternative}] must be one of \texttt{"two.sided"},
\texttt{"greater"} or \texttt{"less"}.  You can specify just the
initial letter.  This parameter indicates the alternative
hypothesis.
\item[\texttt{mu}] a number indicating the true value of the mean (or
difference in means if you are performing a two sample test).
\item[\texttt{paired}] a logical indicating whether you want a paired
t-test.
\item[\texttt{var.equal}] a logical variable indicating whether to treat the
two variances as being equal. If \texttt{TRUE} then the pooled
variance is used to estimate the variance otherwise the Welch
approximation to the degrees of freedom is used.
\item[\texttt{conf.level}] confidence level of the interval.
\end{ldescription}
\end{Arguments}
\begin{Description}
t.test performs one and two sample t-tests on vectors of data.\end{Description}
\begin{Details}
If \texttt{paired} is \texttt{TRUE} then both \texttt{x} and \texttt{y} must
be specified and they must be the same length.  Missing values are
removed (in pairs if \texttt{paired} is \texttt{TRUE}).  If
\texttt{var.equal} is \texttt{TRUE} then the pooled estimate of the
variance is used. If \texttt{var.equal} is \texttt{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 \texttt{"htest"} containing the following
components:
\begin{ldescription}
\item[\texttt{statistic}] the value of the t-statistic.
\item[\texttt{parameters}] the degrees of freedom for the t-statistic.
\item[\texttt{p.value}] the p-value for the test.
\item[\texttt{conf.int}] a confidence interval for the mean appropriate to
the specified alternative hypothesis.
\item[\texttt{estimate}] the estimated mean or difference in means depending
on whether it was a one-sample test or a two-sample test.
\item[\texttt{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[\texttt{alternative}] a character string describing the alternative
hypothesis.
\item[\texttt{method}] a character string indicating what type of t-test was
performed.
\item[\texttt{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}

