rm(list = ls())
abt <- read.table(
url("http://stat.unm.edu/~fletcher/LLM/DATA/TAB3-1.DAT"),
#"C:\\E-drive\\Books\\ANREG2\\newdata\\TAB21-4.DAT",
#"C:\\E-drive\\Books\\LOGLIN3\\DATA\\Tab3-1.dat",
		  sep="",col.names=c("R","S","A","O","y"))
attach(abt)
abt
#summary(abt)

r=factor(R)
o=factor(O)
s=factor(S)
a=factor(A)

svr <- glm(y ~ r + s + o + a ,family = poisson)
 step(svr,y ~ r*s*o*a, direction="forward")