#
# Epage 137
#
# 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.
# 
#-----

# version$language == "R" for R version$language == NULL for SPlus

if(is.null(version$language) == FALSE){ 
  require(alr3)
}else{
  library(alr3)
}

if(is.null(version$language) == FALSE) data(prodscore)

attach(prodscore)

countyFactor <- factor( County, ordered=FALSE )
yearFactor <- factor( Year, ordered=FALSE ) 

mNH <- lm( Value ~ countyFactor + yearFactor ) # the null hypothesis 
summary(mNH)

mAH <- lm( Value ~ countyFactor + yearFactor + P ) # the alternative hypothesis
summary(mAH)

anova(mNH,mAH)

# Now are the other factor variables important?
#
mCP <- lm( Value ~ countyFactor + P )
mYP <- lm( Value ~ yearFactor + P )
mP  <- lm( Value ~ P )

anova(mCP,mAH) # does the year factor provide information ... yes
anova(mYP,mAH) # does the county factor provide information ... yes 
anova(mP,mAH) # does the country+year factors provide information ... yes