Nonignorable Models for Intermittently Missing Categorical Longitudinal Responses |
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Authors: | Roula Tsonaka Dimitris Rizopoulos Geert Verbeke Emmanuel Lesaffre |
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Institution: | 1. Interuniversity Institute for Biostatistics and Statistical Bioinformatics, Katholieke Universiteit Leuven, Kapucijnenvoer 35, Blok D, bus 7001, 3000 Leuven, Belgium;2. Department of Biostatistics, Erasmus Medical Center, PO Box 2040, 3000 CA Rotterdam, the Netherlands |
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Abstract: | Summary A class of nonignorable models is presented for handling nonmonotone missingness in categorical longitudinal responses. This class of models includes the traditional selection models and shared parameter models. This allows us to perform a broader than usual sensitivity analysis. In particular, instead of considering variations to a chosen nonignorable model, we study sensitivity between different missing data frameworks. An appealing feature of the developed class is that parameters with a marginal interpretation are obtained, while algebraically simple models are considered. Specifically, marginalized mixed‐effects models ( Heagerty, 1999 , Biometrics 55, 688–698) are used for the longitudinal process that model separately the marginal mean and the correlation structure. For the correlation structure, random effects are introduced and their distribution is modeled either parametrically or non‐parametrically to avoid potential misspecifications. |
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Keywords: | Categorical responses Constrained vertex‐exchange method Marginalized models Non‐parametric maximum likelihood Selection model Shared parameter model |
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