In addition to evaluating the performance of individual companies, securities analysts also evaluate and compare industry sectors. One of the variables used in this analysis is the percentage growth in net incomes for the previous year. The table, extracted from Forbes

(Jan. 10, 2000), lists the percentage growth in net income for samples of firms from the banking and energy sectors of the U.S. economy.

a. Suppose you want to compare the mean growth in net incomes for the banking and energy sectors. What assumption about the variability in growth rates must be true for the inference about the means to be valid?

b. What are the appropriate null and alternative hypotheses to use in comparing the variability of net income growth rates of the banking and energy sectors?

c. Conduct the test of part b using a = .05. Interpret your results in the context of the problem.

d. What assumptions must hold to ensure the validity of the test?