# SalesDW Example
# Use Durbin-Watson Test to test for 
# uncorrelated residuals.

# install.packages("car")
library(car)

# Create data frame
salesdw <- read.table("c:/datasets/sales.txt", header=T)

# Create simple linear regression model
model <- lm(sales ~ t, data=salesdw)
print(summary(model))

# Obtain Durbin-Watson statistic and p-value
durbinWatsonTest(model)

pdf("c:/datasets/salesdw-resid2.pdf")

p = predict(model)
r = resid(model)
plot(p, r, main="SalesDW Example -- Durbin-Watson Test",
   xlab="Predicted Value", ylab="Residual")
abline(h=0, lty="dashed", col="red")

dev.off( )