# Question

Repeat Exercise 17.19, but using a second-order model with interaction. Interpreting the R2 value, to what extent has inclusion of the squared terms improved the model’s explanatory power?

In exercise

For the Car and Driver information described in Exercise 17.9, it would seem reasonable that the number of seconds required to accelerate to 60 mph would depend on both a car’s weight and its horsepower. Further, it would be logical to assume that horsepower and weight might interact. Using data file XR17009, with y = 0–60 mph acceleration time (seconds), x1 = horsepower, and x2 = curb weight (pounds), fit a model of the form E(y) = β0 + β1x1 + β2x2 + β3x1x2. Interpret the R2 value for the model and indicate whether, at the 0.02 level, the model is significant.

In exercise

For the Car and Driver information described in Exercise 17.9, it would seem reasonable that the number of seconds required to accelerate to 60 mph would depend on both a car’s weight and its horsepower. Further, it would be logical to assume that horsepower and weight might interact. Using data file XR17009, with y = 0–60 mph acceleration time (seconds), x1 = horsepower, and x2 = curb weight (pounds), fit a model of the form E(y) = β0 + β1x1 + β2x2 + β3x1x2. Interpret the R2 value for the model and indicate whether, at the 0.02 level, the model is significant.

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