The Milk data frame has 1337 rows and 4 columns.
This data frame contains the following columns:
a numeric vector giving the protein content of the milk.
a numeric vector giving the time since calving (weeks).
an ordered factor giving a unique identifier for each cow.
a factor with levels
barley,
barley+lupins, and
lupins identifying the diet for each cow.
Diggle, Liang, and Zeger (1994) describe data on the protein content of cows' milk in the weeks following calving. The cattle are grouped according to whether they are fed a diet with barley alone, with barley and lupins, or with lupins alone.