Residual Plot A scatterplot is a plot of the paired (x, y) sample data. A residual plot is a graph of the points with the same x-coordinates, but the corresponding y-coordinates are the residual values. To construct a residual plot, use the same x-axis as the scatterplot, but use a vertical axis of residual values. Draw a horizontal reference line through the residual value of 0, then plot the paired values of (x, residual). Residual plots are helpful in identifying patterns suggesting that the relationship between the variables is not linear, or that the assumption of constant variances is not satisfied.

Construct a residual plot for the data in Table 9-1. Are there any noticeable patterns?