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Peer-Reviewed Publication
Biometrika2026;113(2):asag017.January 1, 2026Journal Article

Comparing causal parameters with many treatments and positivity violations.

A McClean1, Y Li1, S Bae, M McAdams DeMarco2, I Díaz3, W Wu4
1Artificial Intelligence Department, Ataraxis AI, 1239 Broadway, Suite 1502, New York, New York 10001, U.S.A.
2Department of Surgery, New York University, 1 Park Avenue, New York, New York 10016, U.S.A.  yiting.li@nyulangone.org  sunjae.bae@nyulangone.org  mara.mcadamsdemarco@nyulangone.org.
3Division of Biostatistics, New York University, 180 Madison Avenue, New York, New York 10016, U.S.A  ivan.diaz@nyu.edu.
4Department of Health Policy and Management, Johns Hopkins Bloomberg School of Public Health, 2024 E Monument Street, Baltimore, Maryland 21205, U.S.A  wenbowu@jhu.edu.

Abstract

Comparing outcomes across treatments is essential in medicine and public policy. To do so, researchers typically estimate a set of parameters, possibly counterfactual, each targeting adifferent treatment. Treatment-specific means are commonly used, but their identification requires a positivity assumption: every subject has a nonzero probability of receiving each treatment. This assumption is ofte…

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