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Unbiased Regression-Adjusted Estimation of Average Treatment Effects in Randomized Controlled Trials

Alberto Abadie, Mehrdad Ghadiri, Ali Jadbabaie, Mahyar JafariNodeh

arXiv 5 Nov 2025 · Econometrics

arXiv:2511.03236 · PDF · DOI · OpenAlex · Extracted main text

Abstract

This article introduces a leave-one-out regression adjustment estimator (LOORA) for estimating average treatment effects in randomized controlled trials. The method removes the finite-sample bias of conventional regression adjustment and provides exact variance expressions for LOORA versions of the Horvitz-Thompson and difference-in-means estimators under simple and complete random assignment. Ridge regularization limits the influence of high-leverage observations, improving stability and precision in small samples. In large samples, LOORA attains the asymptotic efficiency of regression-adjusted estimator as characterized by Lin (2013, Annals of Applied Statistics), while remaining exactly unbiased. To construct confidence intervals, we rely on asymptotic variance estimates that treat the estimator as a two-step procedure, accounting for both the regression adjustment and the random assignment stages. Two within-subject experimental applications that provide realistic joint distributions of potential outcomes as ground truth show that LOORA eliminates substantial biases and achieves close-to-nominal confidence interval coverage.

Citation extraction

32
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Most heavily cited references

The works this paper leans on most, across its whole bibliography — not restricted to papers in our corpus. Ranked by composite intensity, which combines how often a work is mentioned, how many sections mention it, and how much of that falls in the main text rather than the appendix.

ReferenceIntensityMentionsSectionsMain text
1Lin, Winston (2013) Agnostic notes on regression adjustments to experimental data: reexamining Freedman's critique1.000258100%
2Ghadiri, Mehrdad and Arbour, David and Mai, Tung and Musco, Cameron… (2023) Finite population regression adjustment and non-asymptotic guarantees for treatment effect estimation self0.87492100%
3Harshaw, Christopher and Sävje, Fredrik and Spielman, Daniel A and Z… (2024) Balancing covariates in randomized experiments with the Gram–Schmidt walk design0.87452100%
4Jann Spiess (2025) Optimal estimation when researcher and social preferences are misaligned0.87452100%
5Cytrynbaum, Max (2024) Covariate adjustment in stratified experiments0.84333100%
6Chang, Haoge and Middleton, Joel A and Aronow, PM (2024) Exact bias correction for linear adjustment of randomized controlled trials0.64422100%
7Aronow, Peter M and Middleton, Joel A (2013) A class of unbiased estimators of the average treatment effect in randomized experiments0.58531100%
8Allcott, Hunt and Taubinsky, Dmitry (2015) Evaluating behaviorally motivated policy: Experimental evidence from the lightbulb market0.51121100%
9Billingsley, P (2012) Probability and Measure0.51121100%
10Freedman, David A (2008) On regression adjustments to experimental data0.51121100%

Showing the top 10 of 32 scored citations.

Cited by, within the corpus

arXiv econ.EM papers that cite this one, ranked by how heavily they lean on it.

Citing paperIntensityMentionsSections
1Covariate Adjustment in Randomized Experiments Motivated by Higher-Order Influence Functions0.58531
2Assumption-lean covariate adjustment under covariate adaptive randomization when $p = o (n)$0.40511