set.seed(12345)
x <- rnorm(400,550,100)
x <- round(x,0)
cutpoint <- 650
y <- .98*x + (ifelse(x>cutpoint,30,0)) + round(rnorm(400,0,30),0)
y <- round(y,0)
x.1 <- subset(x, x<=cutpoint)
y.1 <- subset(y, x<=cutpoint)
T <- ifelse(x>cutpoint,1,0)
fit.1 <- lm(y.1~x.1)
x.2 <- subset(x, x >cutpoint)
y.2 <- subset(y, x>cutpoint)
fit.2 <- lm(y.2~x.2)
plot(x.1,y.1,xlim=c(150,900),ylim=c(150,800),pch=1,xlab="Assignment Variable Scores",ylab="Posttest Scores")
points(x.2,y.2,pch=16)
curve(coef(fit.1)[1] + coef(fit.1)[2]*x,xlim=c(150,cutpoint),col="red",add=TRUE)
curve(coef(fit.2)[1] + coef(fit.2)[2]*x,xlim=c(cutpoint,800),col="blue",add=TRUE)
abline(v=cutpoint)
PSAT <- data.frame(x,y,T)
write.table(PSAT,"PSAT.txt",row.names=F)