diet <- dotna( read.table("diet.dat", header = T) )
diet$trt <- factor(diet$trt)
diet$block <- factor(diet$block)
#
# ordinary anova
diet.fit <- aov(dmi ~ trt, diet)

# ancova with covar = first 3 weeks dmi
diet.cov <- lm(dmi ~ covar + trt, diet, na.action=na.omit)

# ancova with blocking and weighting by number of weeks on trial
diet.blk <- lm(dmi ~ covar + block + trt, diet,
   weights=diet$weeks, na.action=na.omit)