The following table gives data on 81 cars about MPG (average miles per gallons), HP (engine horsepower), VOL (cubic feet of cab space), SP (top speed, miles per hour), and WT (vehicle weight in 100 lbs.).

a. Consider the following model:

MPG_i = β₁ + β₂SP_i + β₃HP_i + β₄WT_i + u_i

Estimate the parameters of this model and interpret the results. Do they make economic sense?

b. Would you expect the error variance in the preceding model to be heteroscedastic? Why?

c. Use the White test to find out if the error variance is heteroscedastic.

d. Obtain White’s heteroscedasticity-consistent standard errors and t values and compare your results with those obtained from OLS.

e. If heteroscedasticity is established, how would you transform the data so that in the transformed data the error variance is homoscedastic? Show the necessary calculations.