chew <- read.table("chew.dat",header=T)
 
chew$trt <- factor(chew$trt)
chew$hc <- factor(chew$hc)
chew$time <- factor(chew$time)
chew$diet <- factor(chew$diet)

chew.eat1 <- lm(eat~alfa,chew[chew$time==1,])
chew.eat2 <- lm(eat~alfa,chew[chew$time==2,])