## ----------------------------------------------------------------------------
##   R scripts for Haerdle/Mueller/Sperlich/Werwatz: "Nonparametric and
##   Semiparametric Modelling", Springer Series in Statistics, 2004
## ----------------------------------------------------------------------------
##   Script      SPMcps85lin
## ----------------------------------------------------------------------------
##   Description computes a linear regression of log wages on 
##               schooling, experience and experience squared for 
##               observations from the 1985 CPS (see Berndt, 1991).
##               The marginal wage-schooling and wage-experience 
##               profiles and the 3d wage-schooling/experience surface 
##               are displayed. 
## ----------------------------------------------------------------------------
##   Author      Marlene Mueller, 2008/11/19
## ----------------------------------------------------------------------------

library(scatterplot3d)
library(AER)

data("CPS1985")

l  <- lm( log(wage) ~ education + experience + I(experience^2), data=CPS1985)
summary(l)

b  <- coef(l)

m.school <- data.frame(CPS1985$education,CPS1985$education*b["education"])
m.school <- m.school[order(CPS1985$education),]           # wage-schooling profile

m.experi <- data.frame(CPS1985$experience,
                       CPS1985$experience*b["experience"]
                       +CPS1985$experience^2*b["I(experience^2)"])
m.experi <- m.experi[order(CPS1985$experience),]          # wage-experience profile

par(mfrow=c(1,2))
plot(m.school,col="blue",pch=19,main="Wage <-- Schooling",xlab="education",ylab="")
lines(m.school,col="blue")
plot(m.experi,col="magenta",pch=19,main="Wage <-- Experience",xlab="experience",ylab="")
lines(m.experi,col="magenta")
par(mfrow=c(1,1))

col <- rep("green",nrow(CPS1985)); col[CPS1985$education==12] <- "red"
pch <- rep(1,nrow(CPS1985)); pch[CPS1985$education==12] <- 8

scatterplot3d(CPS1985$education,CPS1985$experience, fitted(l),
              xlab="education",ylab="experience",zlab="",
              main="Wage <-- Schooling, Experience",color=col,pch=pch,angle=130)


## noe use a more complicated linear model

l1  <- lm( log(wage) ~ education + I(education^2)
          + experience + I(experience^2) + I(experience^3), data=CPS1985)
summary(l1)

col <- rep("green",nrow(CPS1985)); col[CPS1985$education==12] <- "red"
pch <- rep(1,nrow(CPS1985)); pch[CPS1985$education==12] <- 8

scatterplot3d(CPS1985$education,CPS1985$experience, fitted(l1),
              xlab="education",ylab="experience",zlab="",
              main="Wage <-- Schooling, Experience",color=col,pch=pch,angle=130)