[R-sig-teaching] Comparing two Regression Lines

[Nagle, Nicholas]

Try this for starters:

X1<-c(25, 50, 100, 200, 400)
Y1<-c(77.7, 78, 64.3, 59.7, 51.2)

X2<-c(25, 50, 100, 200)
Y2<-c(77.7, 52.3, 23.7, 6)

dat1 <- data.frame(X=X1,Y=Y1,f='D1')
dat2 <- data.frame(X=X2,Y=Y2,f='D2')

dat <- rbind(dat1,dat2)

model <- lm(Y~X*f,data=dat)
summary(model)
# Test H_0: fD2=0 for difference in intercept
# Test H_0: X:fD2=0 for difference in slopes.

# Don't forget this test!
anova(lm(Y~X,data=dat),lm(Y~X*f,data=dat))

library(ggplot2)
ggplot(data=dat,aes(x=X,y=Y,group=f))+geom_point(aes(colour=f))+xlim(0,400)+geom_abline(intercept=77.175,slope=-0.07094)+geom_abline(intercept=(77.175-1.54022), slope=(-.07094-.30997))



Nicholas