Consider the follow ing sample regressions fo r the linear, the quadratic, and the cubic models along w ith their respective R2 and adjusted R2.

Linear Quadratic Cubic Intercept 9.66 10.00 10.06 X 2.66 2.75 1.83 X2 NA − 0.31 − 0.33 X3 NA NA 0.26 R2 0.810 0.836 0.896 Adjusted R2 0.809 0.833 0.895

a. Predict y fo r x = 1 and 2 w ith each of the estimated models.

b. Select the m ost appropriate model. Explain.