\Header{trees}{Girth, Height and Volume for Black Cherry Trees}
\keyword{datasets}{trees}
\begin{Description}\relax
This data set provides measurements of the girth, height and volume
of timber in 31 felled black cherry trees.  Note that girth is the
diameter of the tree (in inches) measured at 4 ft 6 in above the
ground.
\end{Description}
\begin{Usage}
\begin{verbatim}data(trees)\end{verbatim}
\end{Usage}
\begin{Format}\relax
A data frame with 31 observations on 3 variables.
\Tabular{rlll}{
\code{[,1]} & \code{Girth} & numeric
& Tree diameter in inches\\
\code{[,2]} & \code{Height}& numeric
& Height in ft\\
\code{[,3]} & \code{Volume}& numeric
& Volume of timber in cubic ft\\}
\end{Format}
\begin{Source}\relax
Ryan, T. A., Joiner, B. L. and Ryan, B. F. (1976)
\emph{The Minitab Student Handbook}.
Duxbury Press.
\end{Source}
\begin{References}\relax
Atkinson, A. C. (1985)
\emph{Plots, Transformations and Regression}.
Oxford University Press.
\end{References}
\begin{Examples}
\begin{ExampleCode}
data(trees)
pairs(trees, panel = panel.smooth, main = "trees data")
plot(Volume ~ Girth, data = trees, log = "xy")
coplot(log(Volume) ~ log(Girth) | Height, data = trees,
       panel = panel.smooth)
summary(fm1 <- lm(log(Volume) ~ log(Girth), data = trees))
summary(fm2 <- update(fm1, ~ . + log(Height), data = trees))
step(fm2)
## i.e., Volume ~= c * Height * Girth^2  seems reasonable
\end{ExampleCode}
\end{Examples}

