The file measles. dat contains data consistent with that obtained in a survey of parents whose children had not been immunized for measles during a recent campaign to immunize all children between the ages of 11 and 15. During the campaign, 7633 children from the 46 schools in the area were immunized; 9962 children whose records showed no previous immunization were not immunized. In a follow-up survey to explore why the children had not been immunized during the campaign, Roberts et al. (1995) sent questionnaires to the parents of a cluster sample of the 9962 children. Ten schools were randomly selected, then a sample of the Mi non immunized children from each school was selected and the parents of those children were sent a questionnaire. Not all parents responded to the questionnaire; you will examine the effects of nonresponse in Exercise 13 of Chapter 8. a Estimate, separately for each school, the percentage of parents who returned a consent form (variable returned ). For this exercise, treat the "no answer" responses (value 9) as not returned. b Using the number of respondents in school i as mi, construct the sampling weight for each observation. c Estimate the overall percentage of parents who received a consent form along with a 95% CI. d How do your estimate and interval in part (c) compare with the results you would have obtained if you had ignored the clustering and analyzed the data as an SRS