STOR Colloquium; Xiao-Li Meng, Harvard
Dissecting Multiple Imputation from a Multi-phase Inference Perspective:
What Happens When God’s, Imputer’s and Analyst’s Models Are Uncongenial?
Department of Statistics, Harvard University
This talk is based on a discussion paper (Xia and Meng, Statistica Sinica, 2017, pp1485-1594) with the same title and the following abstract:
“Real-life data are almost never really real. By the time the data arrive at an investigator’s desk or disk, the raw data, however defined, have most likely gone through at least one “cleaning” process, such as standardization, re-calibration, imputation, or de-sensitization. Dealing with such a reality scientifically requires a more holistic multi-phase perspective than is permitted by the usual framework of “God’s model versus my model.” This article provides an in-depth look, from this broader perspective, into multiple-imputation (MI) inference (Rubin (1987)) under uncongeniality (Meng (1994)). We present a general estimating-equation decomposition theorem, resulting in an analytic (asymptotic) description of MI inference as an integration of the knowledge of the imputer and the analyst, and establish a characterization of self-efficiency (Meng (1994)) for regulating estimation procedures. These results help to reveal how the quality of and relationship between the imputer’s model and analyst’s procedure affect MI inference, including how a seemingly perfect procedure under the “God-versus-me” paradigm is actually inadmissible when God’s, imputer’s, and analyst’s models are uncongenial to each other. Our theoretical investigation also leads to useful procedures that are as trivially implementable as Rubin’s combining rules, yet with confidence coverage guaranteed to be minimally the nominal level, under any degree of uncongeniality. We reveal that the relationship is very complex between the validity of approaches taken for individual phases and the validity of the final multi-phase inference, and indeed that it is a nontrivial matter to quantify or even qualify the meaning of validity itself in such settings. These results and many open problems are presented to raise the general awareness that the multi-phase inference paradigm is an uncongenial forest populated by thorns, as well as some fruits, many of which are still low-hanging.”