#### Splus code to illustrate the  various contrast options.

#### There are four sorts of contrasts available:

#### 1. sum
#### 2. treatment
#### 3. helmert (the default)
#### 4. poly

#### Make some data for example purposes

gender <- factor(c("Male","Male","Male","Female","Female","Female"))
educ   <- ordered(c("Low","Medium","High","Low","Medium","High"),levels=
c("Low","Medium","High"))
y <- c(1,4,3,1,4,7)


contrasts(C(educ,treatment))
contrasts(C(educ,sum))
contrasts(C(educ,helmert))
contrasts(C(educ,poly,2))


model.matrix(y ~ gender + C(educ,treatment))
model.matrix(y ~ gender + C(educ,sum))
model.matrix(y ~ gender + C(educ,helmert))
model.matrix(y ~ gender + C(educ,poly,2))

round(summary(lm(y ~ gender + C(educ,treatment)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,sum)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,helmert)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,poly,2)))$correlation,3)


gender <- factor(c("Male","Male","Male","Female","Female","Female","Female"))
educ   <- ordered(c("Low","Medium","High","Low","Medium","High","Low"),levels=
c("Low","Medium","High"))

y <- c(1,4,3,1,4,7,5)

round(summary(lm(y ~ gender + C(educ,treatment)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,sum)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,helmert)))$correlation,3)
round(summary(lm(y ~ gender + C(educ,poly,2)))$correlation,3)