#Variability around ybar and around the fitted line:
#Access the data:
a <- read.table("http://www.stat.ucla.edu/~nchristo/statistics13/soil_complete.txt", header=TRUE)

#Run simple regression of log(lead) on log(zinc):
q <- lm(log(a$lead) ~ log(a$zinc))

#Construct the scatterplot of log(lead against log(zinc) and show the fitted line and the ybar line:

#Scatterplot:
plot(log(a$zinc), log(a$lead), pch=19)

#Add fitted line"
abline(q)

#Add yabr line:
abline(h=mean(log(a$lead)))

#Show variability around ybar line:
segments(log(a$zinc),log(a$lead), log(a$zinc), mean(log(a$lead)))

#Show variability around fitted line:
segments(log(a$zinc),log(a$lead), log(a$zinc), q$coef[1]+q$coef[2]*log(a$zinc), col="blue", lwd=5)

arrows(4.65,4.82, 4.86,5.05, angle=10, length=.15)
text(5.0,5.10, "mean(log(a$lead))")


#What do you observe?