#
# 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)
}

data(BGSboys)
attach(BGSboys)

# Lets start with forward selection for this problem:

m0 <- lm( HT18 ~ +1 )
m1 <- lm( HT18 ~ +1+WT2+HT2+WT9+HT9+LG9+ST9 )

if(is.null(version$language) == FALSE) {require (xtable); xtable(m1)} else m1

ansf1 <- step(m0,scope=list(lower=~+1, upper=~+1+WT2+HT2+WT9+HT9+LG9+ST9),
                direction="forward", data=BGSboys)

ansf2 <- step(m1,scope=list(lower=~+1, upper=~+1+WT2+HT2+WT9+HT9+LG9+ST9),
                direction="backward", data=BGSboys)