arXiv subjects

Antonio Olivas-Martinez

Publications and source records attributed to Antonio Olivas-Martinez.

3 recordsLinked to original sources

arXiv2025

Proximal Causal Inference for Modified Treatment Policies

The proximal causal inference framework enables the identification and estimation of causal effects in the presence of unmeasured confounding by leveraging two disjoint sets of observed strong proxies: negative control treatments and negative control outcomes. In the point exposure setting, this framework has primarily been applied to estimands comparing counterfactual outcomes under a static fixed intervention or, possibly randomized, regime that depends on baseline covariates. For continuous exposures, alternative hypothetical scenarios can enrich our understanding of causal effects, such as those where each individual receives their observed treatment dose modified in a pre-specified manner - commonly referred to as modified treatment regimes. In this work, we extend the proximal causal inference framework to identify and estimate the mean outcome under a modified treatment regime, addressing this gap in the literature. We propose a flexible strategy that does not rely on the assumption that all confounders have been measured - unlike existing estimators - and leverages modern debiased machine learning techniques using non-parametric estimators of nuisance functions to avoid restrictive parametric assumptions. Our methodology was motivated by immunobridging studies of COVID-19 vaccines aimed at identifying correlates of protection, where the individual's underlying immune capacity is an important unmeasured confounder. We demonstrate its applicability using data from such a study and evaluate its finite-sample performance through simulation studies.

stat.ME↗

arXiv2025

A General Framework for Designing and Evaluating Active-Controlled Trials with Non-Inferiority Objectives

Active-controlled trials with non-inferiority objectives are often used when effective interventions are available, but new options may offer advantages or meet public health needs. In these trials, participants are randomized to an experimental intervention or an active control. The traditional non-inferiority criterion requires that the new intervention preserve a substantial proportion of the active control effect. A key challenge is the absence of a placebo arm, which necessitates reliance on historical data to estimate the active control effect and assumptions about how well this effect applies to the target population. Another challenge arises when the active control is highly effective, as the new intervention may still be valuable even if it does not meet the traditional criterion. This has motivated alternative criteria based on sufficient efficacy relative to a hypothetical placebo. In this work, we propose a general framework for designing and evaluating non-inferiority trials that integrates all existing analytical methods and accommodates both traditional and alternative success criteria. The framework enables the systematic comparison of methods in terms of type I error, power, and robustness to misspecification of the active control effect. We illustrate its applicability in the design of a future HIV prevention trial with a highly effective active control. In this application, our framework identifies methods that provide greater efficiency and robustness than commonly used approaches and demonstrates practical advantages of the alternative non-inferiority criterion. Overall, this framework offers a comprehensive toolkit for rigorous non-inferiority trial design, supporting method selection and the evaluation of new interventions.

stat.ME↗

arXiv2025

Source-Condition Analysis of Kernel Adversarial Estimators

In many applications, the target parameter depends on a nuisance function defined by a conditional moment restriction, whose estimation often leads to an ill-posed inverse problem. Classical approaches, such as sieve-based GMM, approximate the restriction using a fixed set of test functions and may fail to capture important aspects of the solution. Adversarial estimators address this limitation by framing estimation as a game between an estimator and an adaptive critic. We study the class of Regularized Adversarial Stabilized (RAS) estimators that employ reproducing kernel Hilbert spaces (RKHSs) for both estimation and testing, with regularization via the RKHS norm. Our first contribution is a novel analysis that establishes finite-sample bounds for both the weak error and the root mean squared error (RMSE) of these estimators under interpretable source conditions, in contrast to existing results. Our second contribution is a detailed comparison of the assumptions underlying this RKHS-norm-regularized approach with those required for (i) RAS estimators using $\mathcal{L}^2$ penalties, and (ii) recently proposed, computationally stable Kernel Maximal Moment estimators.

math.ST↗