Use the second-order polynomial regression model from Exercise 12-4,

(a) Find a 95% confidence interval on both the first-order and the second-order term in this model.

(b) Is zero in the confidence interval you found for the second-order term in part (a)? What does that fact tell you about the contribution of the second-order term to the model?

(c) Refit the model with only the first-order term. Find a 95% confidence interval on this term. Is this interval longer or shorter than the confidence interval that you found on this term in part (a)?

Exercise 12-4

Hsuie, Ma, and Tsai (€˜€˜Separation and Characterizations of Thermotropic Copolyesters of p-Hydroxybenzoic Acid, Sebacic Acid, and Hydroquinone,€™€™ (1995, Vol. 56) studied the effect of the molar ratio of sebacic acid (the regressor) on the intrinsic viscosity of copolyesters (the response). The following display presents the data.

Ratio Viscosity 0.45 1.0 0.9 0.20 0.34 0.8 0.7 0.58 0.70 0.6 0.5 0.57 0.55 0.4 0.3 0.44