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Title: Improving tests for missing-not-at-random using design of experiments Authors:  Jack Noonan - Cardiff University (United Kingdom) [presenting]
Abstract: Missing data is known to be an inherent and pervasive problem in the process of data collection. The effects are wide-ranging and the loss of data can lead to inefficiencies and introduce bias into analyses. The specific problem of data missing not at random (MNAR) is known to be one of the most complex and challenging problems to handle in this area and testing its prevalence is of great importance. The presence of MNAR missingness can only be tested using a follow-up sample of the missing observations and therefore recovering a proportion of missing values in an efficient way could be crucial in saving the experimenters costs and time and may result in new treatments/technology reaching the public faster. We demonstrate the use of experimental design for developing a strategy to allow researchers to be in a position to be well informed about whether MNAR is a credible issue. Within a linear regression setting, we provide a proof of concept example and, using a number of newly developed approximations for the power of MNAR missingness tests, provide a number of recommendations on how the follow-up sample should be designed.