The U.S. Energy Information Administration publishes summary statistics concerning the energy sector of the U.S. economy. The electric power industry continues to grow. Electricity generation and sales rose to record levels. The file entitled Energy presents the revenue from retail sales ($million) and the net generation by energy source for the period 1993–2004.

a. Produce the correlation matrix of all the variables.

Predict the variables that will remain in the estimated regression equation if standard stepwise regression is used to predict the revenues from retail sales of energy.

b. Use standard stepwise regression to develop an estimate of a model that is to predict the revenue from retail sales of energy ($million).

c. Compare the results of parts a and

b. Explain any difference between the two models.