The Department of Energy and the U.S. Environmental Protection Agency’s 2012 Fuel Economy Guide provides fuel efficiency data for 2012 model year cars and trucks (Department of Energy website, April 16, 2012). The file named 2012 FuelEcon provides a portion of the data for 309 cars. The column labeled Manufacturer shows the name of the company that manufactured the car; the column labeled Displacement shows the engine’s displacement in liters; the column labeled Fuel shows the required or recommended type of fuel (regular or premium gasoline); the column labeled Drive identifies the type of drive (F for front wheel, R for rear wheel, and A for all wheel); and the column labeled Hwy MPG shows the fuel efficiency rating for highway driving in terms of miles per gallon.
a. Develop an estimated regression equation that can be used to predict the fuel efficiency for highway driving given the engine’s displacement. Test for significance using α = .05.
b. Consider the addition of the dummy variable FuelPremium, where the value of FuelPremium is 1 if the required or recommended type of fuel is premium gasoline and 0 if the type of fuel is regular gasoline. Develop the estimated regression equation that can be used to predict the fuel efficiency for highway driving given the engine’s displacement and the dummy variable FuelPremium.
c. Use α = .05 to determine whether the dummy variable added in part (b) is significant.
d. Consider the addition of the dummy variables FrontWheel and RearWheel. The value of FrontWheel is 1 if the car has front wheel drive and 0 otherwise; the value of RearWheel is 1 if the car has rear wheel drive and 0 otherwise. Thus, for a car that has all-wheel drive, the value of FrontWheel and the value of RearWheel is 0. Develop the estimated regression equation that can be used to predict the fuel efficiency for highway driving given the engine’s displacement, the dummy variable FuelPremium, and the dummy variables FrontWheel and RearWheel.
e. For the estimated regression equation developed in part (d), test for overall significance and individual significance using α = .05