arXivDaily arXiv每日学术速递 周一至周五更新
arXiv 2007.00725stat.ME
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部分线性模型中介效应的稳健推断

Robust Inference for Mediated Effects in Partially Linear Models

Oliver Hines, Stijn Vansteelandt, Karla Diaz-Ordaz

AI总结:

本文针对部分线性中介模型提出多重稳健 G 估计量与基于 GMM 的正交得分检验,提升了效应推断功效、小样本表现及模型误设下的稳健性。

摘要:

我们在无未测量混杂假设下,考虑暴露变量 X 通过中介变量 M 对结果变量 Y 产生的中介效应,其中中介和结果的条件期望模型为部分线性模型。我们提出用于直接效应和间接效应的 G 估计量,并证明:当 M 的条件均值模型,或 X 与 Y 的条件均值模型被正确设定时,间接效应具有一致的渐近正态性;而对于直接效应,当 Y 的条件均值模型,或 X 与 M 的条件均值模型正确时,也具有一致的渐近正态性。在这一特定情形下,这改进了以往不假设部分线性均值模型的“三重”稳健方法。无中介效应假设的检验本质上存在困难,因为该检验具有复合性质(即 X 对 M 无效应,或 M 对 Y 无效应),因此当两个效应量都较小时会导致检验功效较低。我们利用广义矩估计(GMM)结果构建了一个新的得分检验框架,该框架将无中介效应假设和无直接效应假设作为特例包含在内。所提出的检验依赖于一种用于估计冗余参数的正交估计策略。模拟结果表明,在部分线性情形下,与传统检验相比,基于 GMM 的检验在功效和小样本表现方面更优,并且在模型误设情况下有显著提升。新方法通过对 COPERS 试验数据的中介分析进行了说明,该随机试验研究了一种非药物干预对慢性疼痛患者的影响。实现这些方法的配套 R 包可在 github.com/ohines/plmed 获取。

英文摘要:

We consider mediated effects of an exposure, X on an outcome, Y, via a mediator, M, under no unmeasured confounding assumptions in the setting where models for the conditional expectation of the mediator and outcome are partially linear. We propose G-estimators for the direct and indirect effect and demonstrate consistent asymptotic normality for indirect effects when models for the conditional means of M, or X and Y are correctly specified, and for direct effects, when models for the conditional means of Y, or X and M are correct. This marks an improvement, in this particular setting, over previous `triple' robust methods, which do not assume partially linear mean models. Testing of the no-mediation hypothesis is inherently problematic due to the composite nature of the test (either X has no effect on M or M no effect on Y), leading to low power when both effect sizes are small. We use Generalized Methods of Moments (GMM) results to construct a new score testing framework, which includes as special cases the no-mediation and the no-direct-effect hypotheses. The proposed tests rely on an orthogonal estimation strategy for estimating nuisance parameters. Simulations show that the GMM based tests perform better in terms of power and small sample performance compared with traditional tests in the partially linear setting, with drastic improvement under model misspecification. New methods are illustrated in a mediation analysis of data from the COPERS trial, a randomized trial investigating the effect of a non-pharmacological intervention of patients suffering from chronic pain. An accompanying R package implementing these methods can be found at github.com/ohines/plmed.

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