1## Demo for a Plot of Engel curve in sample space
2
3data(engel)
4
5plot(foodexp ~ income, data = engel, cex= .5, col = "blue",
6     xlab = "Household Income", ylab = "Food Expenditure")
7
8z <- rq(foodexp ~ income, tau= .50, data = engel)# "median line": L1 - regression
9abline(z, col = "dark blue")
10abline(lm(foodexp ~ income, data = engel), lty=2, col="red") #the dreaded ols line
11
12taus <- c(.05,.1,.25,.75,.90,.95)
13nt <- length(taus)
14
15for( i in 1:length(taus)) {
16    abline(rq(foodexp~income, tau=taus[i], data = engel), col="gray")
17}
18
19legend("bottomright",
20       c("L1 (tau = .50)", "OLS", paste("tau= ", formatC(rev(taus)))),
21       col = c("dark blue", "red", rep("gray", nt)),
22       lty = c(1,2, rep(1, nt)),
23       inset = 0.03)
24