MARCH 5, 2021
Ofer Harel, PhD PSTAT®
Department of Statistics
University of Connecticut
About the Presentation: We present a framework for generating multiple imputations for continuous variables when the missing data are assumed to be nonignorably missing. Imputations are generated from more than one imputation model in order to incorporate uncertainty regarding the missing data mechanism. Parameter estimates based on the different imputation models are combined using rules for nested multiple imputation. Through the use of simulation, we investigate the impact of missing data mechanism uncertainty on post-imputation inferences and show that incorporating this uncertainty can increase the coverage of parameter estimates. We apply our method to a longitudinal clinical trial of low-income women with depression where nonignorably missing data were a concern. We show that different assumptions regarding the missing data mechanism can have a substantial impact on inferences. Our method provides a simple approach for formalizing subjective notions regarding nonresponse so that they can be easily stated, communicated, and compared.
About the Presenter: Ofer Harel, Ph.D. is a professor and Director of admission in the Department of Statistics and a (past) principal Investigator in the Institute for Collaboration on Health, Intervention, and Policy (InCHIP) at the University of Connecticut. Dr. Harel received his doctorate in statistics in 2003 from the Pennsylvania State University; where he developed his methodological expertise in the areas of missing data techniques, diagnostic tests, longitudinal studies, Bayesian methods, sampling techniques, mixture models, latent class analysis, and statistical consulting. Dr. Harel received his post-doctoral training at the University of Washington, Department of Biostatistics, where he worked for the Health Services Research & Development (HSR&D) Center of Excellence, VA Puget Sound Healthcare System, and the National Alzheimer’s Coordinating Center (NACC). Dr. Harel has served as a biostatistical consultant nationally and internationally since 1997. Through his collaborative consulting, Dr. Harel has been involved with a variety of research fields including, but not limited to Alzheimer’s, diabetes, nutrition, HIV/AIDS, and alcohol and drug abuse prevention.