\HeaderA{qqt}{Student's t Quantile-Quantile Plot}{qqt}
\keyword{distribution}{qqt}
\begin{Description}\relax
Plots the quantiles of a data sample against the theoretical quantiles of a Student's t distribution.
\end{Description}
\begin{Usage}
\begin{verbatim}qqt(y, df = Inf, ylim = range(y), main = "Student's t Q-Q Plot", 
    xlab = "Theoretical Quantiles", ylab = "Sample Quantiles", plot.it = TRUE, ...) 
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{y}] a numeric vector or array containing the data sample
\item[\code{df}] degrees of freedom for the t-distribution.  The default \code{df=Inf} represents the normal distribution.
\item[\code{ylim}] plotting range for \code{y}
\item[\code{main}] main title for the plot
\item[\code{xlab}] x-axis title for the plot
\item[\code{ylab}] y-axis title for the plot
\item[\code{plot.it}] whether or not to produce a plot
\item[\code{...}] other arguments to be passed to \code{plot}
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
This function is analogous to \code{qqnorm} for normal probability plots.
In fact \code{qqt(y,df=Inf)} is identical to \code{qqnorm(y)} in all respects except the default title on the plot.
\end{Details}
\begin{Value}
A list is invisibly returned containing the values plotted in the QQ-plot:
\begin{ldescription}
\item[\code{x}] theoretical quantiles of the t-distribution
\item[\code{y}] the data sample, same as input \code{y}
\end{ldescription}
\end{Value}
\begin{Author}\relax
Gordon Smyth
\end{Author}
\begin{SeeAlso}\relax
\code{\LinkA{qqnorm}{qqnorm}}
\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
#  See also the lmFit examples

y <- rt(50,df=4)
qqt(y,df=4)
abline(0,1)
\end{ExampleCode}
\end{Examples}