d = read.table("exmp11-01.txt",header=TRUE,sep=",")
d$box = as.factor(d$box)
fit = aov(strength~box,data=d)
summary(fit)
qqnorm(fit$res);qqline(fit$res)
xmean = by(fit$res,d$box,mean)
xmean = c(rep(xmean[1],6),rep(xmean[1],6),rep(xmean[1],6),rep(xmean[1],6))
d2 = data.frame(x=abs(fit$res-xmean),box=d$box)
fit2 = aov(x~box,data=d2)
summary(fit2)
install.packages("car")
library(car)
fit3 = leveneTest(d$strength,d$box,center=mean)
print(fit3)
TukeyHSD(fit)
plot(TukeyHSD(fit))
abline(v=0)