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Noorbaloochi S, Nelson D, Asgharian M. Balancing and elimination of nuisance variables. The international journal of biostatistics. 2010 Jan 1; 6(2):Article 6.
Dimensions for VA is a web-based tool available to VA staff that enables detailed searches of published research and research projects. Addressing covariate imbalance in causal analysis will be reformulated as an elimination of the nuisance variables problem. We show, within a counterfactual balanced setting, how averaging, conditioning, and marginalization techniques can be used to reduce bias due to a possibly large number of imbalanced baseline confounders. The notions of X-sufficient and X-ancillary quantities are discussed and, as an example, we show how sliced inverse regression and related methods from regression theory that estimate a basis for a central sufficient subspace provide alternative summaries to propensity based analysis. Examples for exponential families and elliptically symmetric families of distributions are provided.