# This program reproduces the figures and output of 
# Cod Catch data of Example 6.1 in Bowerman, O'Connell and Koehler
# Created by C. Andy Tsao, 060515

# Change the working directory to where the data is stored
# Load packages 
#      foreign for reading Splus data
#      car for DW test

cod<-read.S("t6-1 cod catch.splus")
dt<-data.frame(y=cod[,1],t=as.integer(row.names(cod)))
dt; attach(dt)

# Polynomial regression of 1st and 2nd order
m1<-lm(y~t);summary(m1);anova(m1);durbin.watson(m1);
plot(t,m1$res)
t2<-t^2;
m2<-lm(y~t+t2);summary(m2);anova(m2);durbin.watson(m2);

rs<-t%%4;   # rs = t mod(4) = remainder of t divided by 4
is.factor(rs);
cs<-as.factor(rs);
summary(cs);summary(rs);

mr<-lm(y~rs); summary(mr);anova(mr);durbin.watson(mr);
mc<-lm(y~cs); summary(mc);anova(mc);durbin.watson(mc);