# R script for the Effect of an Influence Point Example.

x <- c(3, 3.6, 3.7, 4, 4.5)
y <- c(1, 0.9, 1.3, 2.0, 2.2)
model1 <- lm(y ~ x)

x <- c(x, 1)
y <- c(y, 4)
model2 <- lm(y ~ x)

png("c:/datasets/influence-graph.png")
plot(x, y, pch=16, xlim=c(0, 5), ylim=c(0, 5),
   main="Example: Effect of an Influence Point")
abline(model1, col="red", lty=2)
abline(model2, col="red", lty=1)

text(1.7, 4.0, "Influence Point")
text(1.8, 2.7, "Regression line with influence point included")
text(1.8, 0.3, "Regression line with influence point omitted")  

dev.off( )