4
\title{Yields by growing conditions}
6
The \code{Wheat} data frame has 48 rows and 4 columns.
9
This data frame contains the following columns:
12
an ordered factor with levels
13
\code{3} < \code{1} < \code{2} < \code{4} < \code{5} < \code{6} < \code{8} < \code{9} < \code{7} < \code{12} < \code{11} < \code{10}
29
Pinheiro, J. C. and Bates, D. M. (2000), \emph{Mixed-Effects Models in S
30
and S-PLUS}, Springer, New York.