#
# EPage 214 
#
# Written by:
# -- 
# John L. Weatherwax                2009-04-21
# 
# email: wax@alum.mit.edu
# 
# Please send comments and especially bug reports to the
# above email address.
# 
#-----

save_plots = F

library(DAAG)

# Part (a):
# 
nihills.lm = lm( time ~ dist + climb, data=nihills )
nihills2.lm = lm( time ~ dist + climb + dist:climb, data=nihills )
anova( nihills.lm, nihills2.lm )

# Part (b):
#
if( save_plots ){ postscript("../../WriteUp/Graphics/Chapter6/prob_6_res_vs_fitted.eps", onefile=FALSE, horizontal=FALSE) }

plot( nihills2.lm, which=1 )

if( save_plots ){ dev.off() }

# Lets remove the outlieres and then refit the two models:
#
use = ! ( row.names( nihills ) %in% c("Slieve Donard", "Meelbeg Meelmore") )
nihills.lm = lm( time ~ dist + climb, data=nihills[use,] )
nihills2.lm = lm( time ~ dist + climb + dist:climb, data=nihills[use,] )
anova( nihills.lm, nihills2.lm )