Figure 1: Seventh Figure in Lecture 9. This gives side-by-side boxplots of the residuals from the Fourth Figure, where the residuals are broken down by quintile (fifths) of the x values. There are 100 cases in this data set, so each quintile represents 20 values. Thus, if the x values are arranged in ascending order, the residuals corresponding to the smallest are used to construct the box on the left, from the twenty-first through forteith to construct the second one, and so forth and the last box on the right is constructed from the residuals corresponding to the 20 largest x values. Note that except for the last box, the IQR's for each of the boxes is about the same, indicating that the horn shape seen in the Fourth figure is not really so clear as it looks.