Generalizing conditional average treatment effects from nested randomized trials to all trial-eligible individuals

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Hauptverfasser: Wen, Lan, Dahabreh, Issa J., Chiu, Yu-Han
Format: Preprint
Veröffentlicht: 2026
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author Wen, Lan
Dahabreh, Issa J.
Chiu, Yu-Han
author_facet Wen, Lan
Dahabreh, Issa J.
Chiu, Yu-Han
contents Randomized controlled trials often enroll participants whose characteristics differ from those of a target population, which can limit the generalizability of the estimated treatment effects when effect modifiers differ across populations. While existing generalizability methods primarily focus on estimating the average treatment effect (ATE) in the target population, such summaries may obscure important heterogeneity that is relevant for clinical and policy decision-making. In this work, we illustrate an approach for estimating the conditional average treatment effect (CATE) in a target population of trial-eligible individuals as a function of prespecified effect modifiers within a nested trial setting. Our approach combines semiparametric theory with flexible estimation: we first estimate nuisance functions using data-adaptive methods and construct pseudo-outcomes from conditional influence functions, then estimate the CATE function via local linear (kernel) regression. Sample splitting and cross-fitting are used to reduce overfitting bias and ensure asymptotic valid inference. Finite-sample performance is assessed via simulations and illustrated in the Coronary Artery Surgery Study (CASS).
format Preprint
id arxiv_https___arxiv_org_abs_2605_14952
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Generalizing conditional average treatment effects from nested randomized trials to all trial-eligible individuals
Wen, Lan
Dahabreh, Issa J.
Chiu, Yu-Han
Methodology
Applications
Randomized controlled trials often enroll participants whose characteristics differ from those of a target population, which can limit the generalizability of the estimated treatment effects when effect modifiers differ across populations. While existing generalizability methods primarily focus on estimating the average treatment effect (ATE) in the target population, such summaries may obscure important heterogeneity that is relevant for clinical and policy decision-making. In this work, we illustrate an approach for estimating the conditional average treatment effect (CATE) in a target population of trial-eligible individuals as a function of prespecified effect modifiers within a nested trial setting. Our approach combines semiparametric theory with flexible estimation: we first estimate nuisance functions using data-adaptive methods and construct pseudo-outcomes from conditional influence functions, then estimate the CATE function via local linear (kernel) regression. Sample splitting and cross-fitting are used to reduce overfitting bias and ensure asymptotic valid inference. Finite-sample performance is assessed via simulations and illustrated in the Coronary Artery Surgery Study (CASS).
title Generalizing conditional average treatment effects from nested randomized trials to all trial-eligible individuals
topic Methodology
Applications
url https://arxiv.org/abs/2605.14952