Abstract In causal mediation analysis, nonparametric identification of the natural indirect effect typically relies on, in addition to no unobserved pre-exposure confounding, fundamental assumptions of (i) so-called “cross-world-counterfactuals” independence and (ii) no exposure-induced confounding. When the mediator is binary, bounds for partial identification have been given when neither assumption is made, or alternatively when assuming only (ii). We extend existing bounds to the case of a polytomous mediator, and provide bounds for the case assuming only (i). We apply these bounds to data from the Harvard PEPFAR program in Nigeria, where we evaluate the extent to which the effects of antiretroviral therapy on virological failure are mediated by a patient’s adherence, and show that inference on this effect is somewhat sensitive to model assumptions.

中文翻译：

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论自然间接效应的部分识别


摘要 在因果中介分析中，自然间接效应的非参数识别除了没有未观察到的暴露前混杂之外，通常还依赖于以下基本假设：（i）所谓的“跨世界反事实”独立性和（ii）无暴露- 引起的混杂。当中介是二元的时，当没有做出任何假设时，或者当仅假设（ii）时，已经给出了部分识别的界限。我们将现有的边界扩展到多分中介的情况，并为仅假设 (i) 的情况提供边界。我们将这些界限应用于尼日利亚哈佛 PEPFAR 计划的数据，我们评估了抗逆转录病毒治疗对病毒学失败的影响在多大程度上是由患者的依从性介导的，并表明对这种影响的推断对模型假设有些敏感。