\HeaderA{Early}{Early childhood intervention study}{Early}
\keyword{datasets}{Early}
\begin{Description}\relax
Cognitive scores of infants in a study of early childhood
intervention.  The 103 infants from low income African American
families were divided into a treatment group (58
infants) and a control group (45 infants).  Starting at 0.5 years of age
the infants in the treatment group were exposed to an enriched environment.
Each infant's cognitive score on an age-specific, normalized scale was
recorded at ages 1, 1.5, and 2 years.
\end{Description}
\begin{Usage}
\begin{verbatim}data(Early)\end{verbatim}
\end{Usage}
\begin{Format}\relax
This \code{groupedData} object contains the following columns
\describe{
\item[id] An ordered factor of the id number for each infant.
\item[cog] A numeric cognitive score.
\item[age] The age of the infant at the measurement.
\item[trt] A factor with two levels, \code{"N"} and \code{"Y"},
indicating if the infant is in the early childhood intervention
program.
}
\end{Format}
\begin{References}\relax
Singer, Judith D. and Willett, John B. (2003), \emph{Applied
Longitudinal Data Analysis}, Oxford University Press. (Ch. 3)
\end{References}
\begin{Examples}
\begin{ExampleCode}
str(Early)
\end{ExampleCode}
\end{Examples}

