(Continuation of Problem 7.7.) Calculate the variance of CESD for observations in each of the groups defined by income as follows: INCOME <30, INCOME between 30 and 39 inclusive, INCOME between 40 and 49 inclusive, INCOME between 50 and 59 inclusive, INCOME

>59. For each observation, define a variable WEIGHT equal to 1 divided by the variance of a CESD within the income group to which it belongs. Obtain a weighted least squares regression of the untransformed variable CESD on income, using the values of WEIGHT as weights. Compare the results with the unweighted regression analysis. Is the fit improved by weighting?