\HeaderA{nlschools}{Eighth-Grade Pupils in the Netherlands}{nlschools}
\keyword{datasets}{nlschools}
\begin{Description}\relax
Snijders and Bosker (1999) use as a running example a study of 2287
eighth-grade pupils (aged about 11) in 132 classes in 131 schools in
the Netherlands.  Only the variables used in our examples are supplied.
\end{Description}
\begin{Usage}
\begin{verbatim}
nlschools
\end{verbatim}
\end{Usage}
\begin{Format}\relax
This data frame contains 2287 rows and the following columns:
\describe{
\item[\code{lang}] language test score

\item[\code{IQ}] Verbal IQ

\item[\code{class}] class ID

\item[\code{GS}] Class size: number of eighth-grade pupils recorded in the class (there
may be others: see \code{COMB}, and some may have been omitted with missing
values).

\item[\code{SES}] Social-economic status of pupil's family.

\item[\code{COMB}] were the pupils taught in a multi-grade class (\code{0/1})?  Classes which
contained pupils from grades 7 and 8 are coded \code{1}, but only
eighth-graders were tested.
}
\end{Format}
\begin{Source}\relax
Snijders, T. A. B. and Bosker, R. J. (1999)
\emph{Multilevel Analysis. An Introduction to Basic and Advanced Multilevel Modelling.}
London: Sage.
\end{Source}
\begin{References}\relax
Venables, W. N. and Ripley, B. D. (2002)
\emph{Modern Applied Statistics with S.} Fourth edition.  Springer.
\end{References}
\begin{Examples}
\begin{ExampleCode}
library(nlme)
nl1 <- nlschools
attach(nl1)
classMeans <- tapply(IQ, class, mean)
nl1$IQave <- classMeans[as.character(class)]
nl1$IQ <- nl1$IQ - nl1$IQave
detach()
cen <- c("IQ", "IQave", "SES")
nl1[cen] <- scale(nl1[cen], center = TRUE, scale = FALSE)

nl.lme <- lme(lang ~ IQ*COMB + IQave + SES,
              random = ~ IQ | class, data = nl1)
summary(nl.lme)
\end{ExampleCode}
\end{Examples}