12.12 Amalgamated Power, Inc., has asked you to estimate a regression equation to determine the effect of various predictor variables on the demand for electricity sales. You will prepare a series of regression estimates and discuss the results using the quarterly data for electrical sales during the past 17 years in the data file Power Demand.

a. Estimate a regression equation with electricity sales as the dependent variable, using the number of customers and the price as predictor variables.

Interpret the coefficients.

b. Estimate a regression equation (electricity sales)

using only number of customers as a predictor variable. Interpret the coefficient and compare the result to the result from part a.

c. Estimate a regression equation (electricity sales)

using the price and degree days as predictor variables.

Interpret the coefficients. Compare the coefficient for price with that obtained in part a.

d. Estimate a regression equation (electricity sales) using disposable income and degree days as predictor variables. Interpret the coefficients.