This data set provides measurements of the diameter, height and volume of timber in 31 felled black cherry trees. Note that the diameter (in inches) is erroneously labelled Girth in the data. It is measured at 4 ft 6 in above the ground.

`trees`

A data frame with 31 observations on 3 variables.

`[,1]` |
`Girth` |
numeric | Tree diameter (rather than girth, actually) in inches |

`[,2]` |
`Height` |
numeric | Height in ft |

`[,3]` |
`Volume` |
numeric | Volume of timber in cubic ft |

Atkinson, A. C. (1985)
*Plots, Transformations and Regression*.
Oxford University Press.

# NOT RUN { require(stats); require(graphics) 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 # }