HW1:

0.1 Data management

# install.package("mlmRev")
library(mlmRev)

# load the data from the package
data(Gcsemv, package="mlmRev")

0.2 Summary statistics

with(Gcsemv, cor(written, course, use="pairwise"))

[1] 0.47417

# compute the means by school
course_schavg <- with(Gcsemv, tapply(course, school, mean, na.rm=T))
written_schavg <- with(Gcsemv, tapply(written, school, mean, na.rm=T))

cor(course_schavg, written_schavg)

[1] 0.39568

0.3 Visualization

with(Gcsemv, plot(written ~ course, 
                bty = 'n', 
                cex = 0.5,
                xlab = 'course score', 
                ylab = 'written score'))
with(Gcsemv, abline(lm(written ~ course)))
grid()
points(course_schavg, written_schavg, pch=16, col=5)
abline(lm(written_schavg ~ course_schavg), col=5)