#
# Epage 
#
# 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)

# highway data
if(is.null(version$language) == FALSE) data(highway)
a <- highway
a$logADT <- logb(a$ADT,2)
a$logTrks <- logb(a$Trks,2)
a$logLen <- logb(a$Len,2)
a$logSigs1 <- logb((a$Sigs*a$Len+1)/a$Len,2)
a$logRate <- logb(a$Rate,2)
# set the contrasts to the R default
options(contrasts=c(factor="contr.treatment",ordered="contr.poly"))
a$Hwy <- if(is.null(version$language) == FALSE) factor(a$Hwy,ordered=FALSE) else factor(a$Hwy)
attach(a)
names(a)
m1 <- lm(logRate ~ logLen+logADT+logTrks+logSigs1+Slim+Shld+Lane+Acpt+Itg+Lwid+Hwy)
if(is.null(version$language) == FALSE) {require (xtable); xtable(m1)} else m1

# step backwards AIC
m0 <- lm(logRate ~logLen,data=a)

ansf2 <- step(m1,scope=list( lower=~logLen, upper=~logLen+logADT+logTrks+logSigs1+Slim+Shld+Lane+Acpt+Itg+Lwid+Hwy),
              direction="backward", data=a) #, scale=sigma.hat(m1)^2)