\begin{Schunk}
\begin{Sinput}
 ## The "data" folder contains the hbsc data
 ddir <- "data"
 hbsc.complete <- readRDS(file.path(ddir, "hbsc.rds"))
 ## hbsc contains grades 6 and 7 responses
 hbsc <- hbsc.complete[hbsc.complete$Grade %in% c("6", "7"), ]
\end{Sinput}
\end{Schunk}
