R: Log-size of 79 Sitka spruce trees

spruce {geepack} | R Documentation

## Log-size of 79 Sitka spruce trees

### Description

The `spruce` data frame has 1027 rows and 6 columns. The data consists of measurements on 79 sitka spruce trees over two growing seasons. The trees were grown in four controlled environment chambers, of which the first two, containing 27 trees each, were treated with introduced ozone at 70 ppb whilst the remaining two, containing 12 and 13 trees, were controls.

### Usage

    spruce

### Format

This data frame contains the following columns:

chamber

  a numeric vector of chamber numbers

ozone

  a factor with levels `enriched` and `normal`

id

  a numeric vector of tree id

time

  a numeric vector of the time when the measurements were taken, measured in days since Jan. 1, 1988

wave

  a numeric vector of the measurement number

logsize

  a numeric vector of the log-size

### Source

Diggle, P.J., Liang, K.Y., and Zeger, S.L. (1994) Analysis of Longitudinal Data, Clarendon Press.

### Examples

    data(spruce)
    spruce$contr <- ifelse(spruce$ozone=="enriched", 0, 1)
    sitka88 <- spruce[spruce$wave <= 5,]
    sitka89 <- spruce[spruce$wave > 5,]
    fit.88 <- geese(logsize ~ as.factor(wave) + contr +
                              I(time/100*contr) - 1,
                    id=id, data=sitka88, corstr="ar1")
    summary(fit.88)

    fit.89 <- geese(logsize ~ as.factor(wave) + contr - 1,
                    id=id, data=sitka89, corstr="ar1")
    summary(fit.89)

[Package geepack version 1.3-1 Index]