The Spruce data frame has 1027 rows and 4 columns.
Arguments
source
Pinheiro, J. C. and Bates, D. M. (2000), Mixed-Effects Models in S
and S-PLUS, Springer, New York. (Appendix A.28)
Diggle, Peter J., Liang, Kung-Yee and Zeger, Scott L. (1994),
Analysis of longitudinal data, Oxford University Press,
Oxford.
Details
Diggle, Liang, and Zeger (1994, Example 1.3, page 5)
describe data on the growth of spruce trees that have been exposed to
an ozone-rich atmosphere or to a normal atmosphere.