# Question

Refer to the feed efficiency data in Exercise 12.14. The researcher is relating y, feed efficiency, to the explanatory variables: x1, amount of feed additive; and x2, amount of copper placed in the feed. Consider the following models:

Model 1: y = β0 + β1x1 + ɛ

Model 2: y = β0 + β1x1 + β2x2 + ɛ

Model 3: y = β0 + β1x1 + β2x21 + β3x2 + ɛ

Model 4: y = β0 + β1x1 + β2x21 + β3x2 + + β4x1x2 + β5x21x2 ɛ

a. In model 4, which of the coefficients are significantly different from 0 at the .05 level?

b. Do the added terms in model 4 provide a significant gain over model 3 in the fit of the model.

c. Are your conclusions from parts (a) and (b) consistent? Explain in detail.

Model 1: y = β0 + β1x1 + ɛ

Model 2: y = β0 + β1x1 + β2x2 + ɛ

Model 3: y = β0 + β1x1 + β2x21 + β3x2 + ɛ

Model 4: y = β0 + β1x1 + β2x21 + β3x2 + + β4x1x2 + β5x21x2 ɛ

a. In model 4, which of the coefficients are significantly different from 0 at the .05 level?

b. Do the added terms in model 4 provide a significant gain over model 3 in the fit of the model.

c. Are your conclusions from parts (a) and (b) consistent? Explain in detail.

## Answer to relevant Questions

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