Normal Probability Plot of Residuals

The normal probability plot is a graphical tool for comparing a data set with the normal distribution. We can use it with the standardized residual of the linear regression model and see if the error term ϵ is actually normally distributed.

Problem

Create the normal probability plot for the standardized residual of the data set faithful.

Solution

We apply the lm function to a formula that describes the variable eruptions by the variable waiting, and save the linear regression model in a new variable eruption.lm. Then we compute the standardized residual with the rstandard function.

We now create the normal probability plot with the qqnorm function, and add the qqline for further comparison.

Note

Further detail of the qqnorm and qqline functions can be found in the R documentation.