23.

(a) Estimate the variances in Problems 19 through 22.

(b) Determine a 95 percent confidence interval for the variance in the data relating to lung cancer.

(c) Break up the lung cancer data into two parts — the first corresponding to states whose average cigarette consumption is less than 2,300, and the second greater. Assume a linear regression model for both sets of data. How would you test the hypothesis that the variance of a response is the same for both sets?

(d) Do the test in part

(c) at the .05 level of significance.