\Header{qqnorm}{Quantile-Quantile Plots}
\alias{qqline}{qqnorm}
\methalias{qqnorm.default}{qqnorm}
\alias{qqplot}{qqnorm}
\keyword{hplot}{qqnorm}
\keyword{distribution}{qqnorm}
\begin{Description}\relax
\code{qqnorm} is a generic functions the default method of which
produces a normal QQ plot of the values in \code{y}.
\code{qqline} adds a line to a normal quantile-quantile plot which
passes through the first and third quartiles.

\code{qqplot} produces a QQ plot of two datasets.

Graphical parameters may be given as arguments to \code{qqnorm},
\code{qqplot} and \code{qqline}.\end{Description}
\begin{Usage}
\begin{verbatim}
qqnorm(y, ...)
qqnorm(y, ylim, main = "Normal Q-Q Plot",
       xlab = "Theoretical Quantiles",
       ylab = "Sample Quantiles", plot.it = TRUE, ...)
qqline(y, ...)
qqplot(x, y, plot.it = TRUE, xlab = deparse(substitute(x)),
       ylab = deparse(substitute(y)), ...)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] The first sample for \code{qqplot}.
\item[\code{y}] The second or only data sample.
\item[\code{xlab, ylab, main}] plot labels.
\item[\code{plot.it}] logical. Should the result be plotted?
\item[\code{ylim, ...}] graphical parameters.
\end{ldescription}
\end{Arguments}
\begin{Value}
For \code{qqnorm} and \code{qqplot}, a list with components
\begin{ldescription}
\item[\code{x}] The x coordinates of the points that were/would be plotted
\item[\code{y}] The corresponding y coordinates
\end{ldescription}
\end{Value}
\begin{SeeAlso}\relax
\code{\Link{ppoints}}.\end{SeeAlso}
\begin{Examples}
\begin{ExampleCode}
y <- rt(200, df = 5)
qqnorm(y); qqline(y, col = 2)
qqplot(y, rt(300, df = 5))
data(precip)
qqnorm(precip, ylab = "Precipitation [in/yr] for 70 US cities")
\end{ExampleCode}
\end{Examples}

