12.4 Contrasts and the parameters of ANCOVA models

Ancovacontrasts <- read.table("c:\\temp\\Ancovacontrasts.txt",header=T)
attach(Ancovacontrasts)

names(Ancovacontrasts)

lm(weight[sex=="male"]~age[sex=="male"])

lm(weight~age,subset=(sex=="female"))

lm(weight~age)

options(contrasts=c("contr.treatment", "contr.poly"))
model1 <- lm(weight~age*sex)

summary(model1)

options(contrasts=c("contr.helmert", "contr.poly"))
model2 <- lm(weight~age*sex)

summary(model2)

options(contrasts=c("contr.sum", "contr.poly"))
model3 <- lm(weight~age*sex)

summary(model3)