\begin{Schunk}
\begin{Sinput}
 plot(gradrate ~ instcstP1000, data = dat, col = schtype, xlab = "Instructional Cost/1000", ylab = "Graduation Rate", pch = c("o","+")[dat$schtype])
 legend("topleft", legend = levels(dat$schtype), col = c(1,2), pch = c("o","+"))
\end{Sinput}
\end{Schunk}
