15. Using the Sum of Squares Criterion In addition to the value of R2, another measurement used to assess the quality of a model is the sum of squares of the residuals. A residual is the difference between an observed y value and the value of y predicted from the model, which is denoted as . Better models have smaller sums of squares.

Refer to the example in this section.

a. Find the sum of squares of the residuals resulting from the linear model.

b. Find the sum of squares of residuals resulting from the quadratic model.

c. Verify that according to the sum of squares criterion, the quadratic model is better than the linear model.