Inference in the presence of outliers and missing data

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Item nonresponse occurs in most, if not all surveys. Nonresponse is an important problem in surveys because response rates have been decreasing over time. In most cases, item nonresponse is treated by using some form of imputation. Another difficulty that occurs frequently in surveys (especially in business surveys) is the presence of outliers. Nonresponse generally leads to biased estimators if the respondents and nonrespondents have different characteristics with respect to the variables measured by the survey, whereas outliers potentially lead to very unstable estimators. It becomes necessary to develop techniques that reduce the nonresponse bias in the context of nonresponse and the variance in the context of outliers. Among the possible applications, the developed techniques play a central role in evaluating existing theories and they allow the survey statisticians to provide better estimators.