## Girth, Height and Volume for Black Cherry Trees

### Description

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.

### Usage

trees

### Format

A data frame with 31 observations on 3 variables.

`[,1]` | `Girth` | numeric
| Tree diameter in inches |

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

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

### Source

Ryan, T. A., Joiner, B. L. and Ryan, B. F. (1976)
*The Minitab Student Handbook*.
Duxbury Press.

### References

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

### Examples

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