11.78 Refer to Exercise 11.77. The contractor samples 25 recent jobs and fits both the complete second-order model part

(b) and the reduced main effects model in part

(a) so that a test can be conducted to determine whether the additional complexity of the second-order model is necessary. The resulting SSE and are given in the table below.

a Is there sufficient evidence to conclude that the second-order terms are important for predicting the mean cost?

b Suppose the contractor decides to use the main effects model to predict costs. Use the global F-test to determine whether the main effects model is useful for predicting costs.