#
# EPage 240
#
# 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.
# 
#-----

library(DAAG)

# Plot the two sets of elastic bands (from EPage 167):
#
source('../Chapter5/chap_5_prob_1.R')

elastic1$type = 1
elastic2$type = 2

elastic = rbind( elastic1, elastic2 )
elastic$type = as.factor(elastic$type)

# We will comare the regression lines following the models built in 7.3: fitting multiple lines: 
#
elastic.lm1 = lm( distance ~ 1, data=elastic )
elastic.lm2 = lm( distance ~ stretch, data=elastic )
elastic.lm3 = lm( distance ~ stretch + type, data=elastic ) # a different intercept for each set of data (common slope)
elastic.lm4 = lm( distance ~ stretch + type + stretch:type, data=elastic ) # a different slope and intercept for each set of data

# Compare all of the models:
#
anova( elastic.lm1, elastic.lm2, elastic.lm3, elastic.lm4 )

# Lets look for outliers (7 is an outlier): 
plot( elastic.lm2, which=1 )