\HeaderA{ChickWeight}{Weight versus age of chicks on different diets}{ChickWeight}
\keyword{datasets}{ChickWeight}
\begin{Description}\relax
The \code{ChickWeight} data frame has 578 rows and 4 columns from an
experiment on the effect of diet on early growth of chicks.
\end{Description}
\begin{Usage}
\begin{verbatim}ChickWeight\end{verbatim}
\end{Usage}
\begin{Format}\relax
This data frame contains the following columns:
\describe{
\item[weight] a numeric vector giving the body weight of the chick (gm).

\item[Time] a numeric vector giving the number of days since birth when
the measurement was made.

\item[Chick] an ordered factor with levels
\code{18} < \dots < \code{48}
giving a unique identifier for the chick.  The ordering of
the levels groups chicks on the same diet together and
orders them according to their final weight (lightest to
heaviest) within diet.

\item[Diet] a factor with levels 1,\dots,4 indicating which
experimental diet the chick received.

}
\end{Format}
\begin{Details}\relax
The body weights of the chicks were measured at birth and every
second day thereafter until day 20.  They were also measured on day
21.  There were four groups on chicks on different protein diets.
\end{Details}
\begin{Source}\relax
Crowder, M. and Hand, D. (1990), \emph{Analysis of Repeated Measures},
{Chapman and Hall} (example 5.3)

Hand, D. and Crowder, M. (1996), \emph{Practical Longitudinal Data
Analysis}, Chapman and Hall (table A.2)

Pinheiro, J. C. and Bates, D. M. (2000) \emph{Mixed-effects Models in
S and S-PLUS}, Springer.
\end{Source}
\begin{Examples}
\begin{ExampleCode}
require(stats); require(graphics)
coplot(weight ~ Time | Chick, data = ChickWeight,
    type = "b", show.given = FALSE)
## fit a representative chick
fm1 <- nls(weight ~ SSlogis( Time, Asym, xmid, scal ),
    data = ChickWeight, subset = Chick == 1)
summary( fm1 )
\end{ExampleCode}
\end{Examples}

