#
# Epage 65
#
# 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.
# 
#-----

if(is.null(version$language) == FALSE) require(alr3) else library(alr3)
#UN2 <- read.table("data/UN2.txt",header=TRUE)
if(is.null(version$language) == FALSE) data(UN2)
attach(UN2)

# 3.2.1:
#
m = lm( logFertility ~ logPPgdp + Purban )
summary(m)

# get the added-variable plot for the addition of the variable logPPgdp after Purban 
#
m_no_logPPgdp   = lm( logFertility ~ Purban )
r_m_no_logPPgdp = residuals( m_no_logPPgdp ) 

m_logPPgdp_on_Purban   = lm( logPPgdp ~ Purban )
r_m_logPPgdp_on_Purban = residuals( m_logPPgdp_on_Purban ) 

# the added variable plot
plot( r_m_logPPgdp_on_Purban, r_m_no_logPPgdp )

mav = lm( r_m_no_logPPgdp ~ r_m_logPPgdp_on_Purban ) 
round(coef(mav),4)