Document Type thesis Author Name Zong, Yujie URN etd-041511-155723 Title A Sensitivity Analysis of a Nonignorable Nonresponse Model Via EM Algorithm and Bootstrap Degree MS Department Mathematical Sciences Advisors Balgobin Nandram, Advisor Dhiman Bhadra, Advisor Keywords Bivariate binomial distribution Bootstrap EM algorithm Missing not at random Multinomial model 2X2 categorical tables Date of Presentation/Defense 2011-03-28 Availability unrestricted
The Slovenian Public Opinion survey (SPOS), which carried out in 1990, was used by the government of Slovenia as a benchmark to prepare for an upcoming plebiscite, which asked the respondents whether they support independence from Yugoslavia. However, the sample size was large and it is quite likely that the respondents and nonrespondents had divergent viewpoints. We first develop an ignorable nonresponse model which is an extension of a bivariate binomial model. In order to accommodate the nonrespondents, we then develop a nonignorable nonresponse model which is an extension of the ignorable model. Our methodology uses an EM algorithm to fit both the ignorable and nonignorable nonresponse models, and estimation is carried out using the bootstrap mechanism. We also perform sensitivity analysis to study different degrees of departures of the nonignorable nonresponse model from the ignorable nonresponse model. We found that the nonignorable nonresponse model is mildly sensitive to departures from the ignorable nonresponse model. In fact, our finding based on the nonignorable model is better than an earlier conclusion about another nonignorable nonresponse model fitted to these data.
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