#
# Epage 191
#
# Written by:
# -- 
# John L. Weatherwax                2009-04-21
# 
# email: wax@alum.mit.edu
# 
# Please send comments and especially bug reports to the
# above email address.
# 
#-----

# version$language == "R" for R version$language == NULL for SPlus

if(is.null(version$language) == FALSE){ 
  require(alr3)
}else{
  library(alr3)
}

data(stopping)
attach(stopping)

# 


plot( Speed, Distance )

# fit a constant variance model:
# 
m0 <- lm( Distance ~ Speed )
abline(m0) 

# generate residual plots by hand
#
postscript("../../WriteUp/Graphics/Chapter8/prob_4_res_vs_yhat_plot.eps", onefile=FALSE, horizontal=FALSE)
plot(predict(m0),residuals(m0,type="pearson"),xlab="(a) Yhat", ylab="Residuals")
abline(h=0)
dev.off() 

postscript("../../WriteUp/Graphics/Chapter8/prob_4_res_vs_speed_plot.eps", onefile=FALSE, horizontal=FALSE)
plot(Speed,residuals(m0,type="pearson"),xlab="(b) Speed", ylab="Residuals")
abline(h=0)
dev.off()

postscript("../../WriteUp/Graphics/Chapter8/prob_4_res_vs_speed2_plot.eps", onefile=FALSE, horizontal=FALSE)
plot(Speed^2,residuals(m0,type="pearson"),xlab="(c) Speed^2", ylab="Residuals")
abline(h=0)
dev.off()

# score tests, using car
library(car)
s1 <- ncv.test(m0,~Speed,data=stopping)
s2 <- ncv.test(m0,~Speed+I(Speed^2),data=stopping)
s3 <- ncv.test(m0,~I(Speed^2),data=stopping)
s4 <- ncv.test(m0)
ans <- data.frame(
      df=c(s1$Df,s2$Df,s3$Df,s4$Df),
      S=c(s1$ChiSquare,s2$ChiSquare,s3$ChiSquare,s4$ChiSquare),
      p=c(s1$p,s2$p,s3$p,s4$p))
# the next line adds row lables to the output, labelled according to the
# model. This does not work in SPlus because models are lists, and I can't
# figure out how to fix it up.
if(is.null(version$language) == FALSE)
  row.names(ans) <-c(s1$formula, s2$formula, s3$formula, s4$formula)
round(ans,3)