5.5. As discussed in Section 5.4, the imputation method in Problem 5.4 is improper, since it does not propagate the uncertainty in the regression parameter estimates. One way of making it proper is to compute the regression parameters for each set of imputations using a bootstrap sample of the complete cases. Repeat Problem 5.4 with this modification, and compare the resulting multiple imputation intervals. They should be a bit wider than the corresponding intervals from Problem 5.4.