pdf("kuehl_06_07.pdf")

agg <- c(rep(1,6),rep(2,8))
knead <- c(1,1,2,2,2,3,1,1,1,2,2,3,3,3)
strength <- c(106,108,93,101,98,56,107,110,116,63,60,40,41,44)

tensile <- data.frame(agg,knead,strength)
attach(tensile)

agg <- factor(agg,levels=1:2,labels=c("Basalt","Silicious"))
knead <- factor(knead,levels=1:3,labels=c("Regular","Low","Very Low"))

tapply(strength,agg,mean)
tapply(strength,knead,mean)
tapply(strength,list(agg,knead),mean)

options(contrasts=c("contr.sum","contr.poly"))

tensile.mod1 <- aov(strength ~ agg + knead + agg:knead)
summary(tensile.mod1)

library(car)

Anova(tensile.mod1,type="III")

dev.off()