Efficient and flexible estimation of natural direct and indirect effects under intermediate confounding and monotonicity constraints.
Efficient and flexible estimation of natural direct and indirect effects under intermediate confounding and monotonicity constraints.
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在中间混杂和单调性约束下高效灵活地估计自然直接和间接影响。
作者：
Rudolph,KaraE;Williams,Nicholas;Díaz,Iván
自然的直接效应和间接效应是中间指标，它们分解了平均治疗效果，并描述了不同水平的治疗将如何通过介体数值的变化(在间接效应的情况下)或不通过介体数值的诱发变化(在直接效应的情况下)来影响结果。在存在治疗诱导的混杂因素的情况下，自然的直接和间接影响通常不是点识别的；然而，如果愿意承担治疗和治疗诱导的混杂因素之间的单调性，它们可以被识别。我们认为，在相对常见的鼓励设计试验环境中，这一假设可能是合理的，其中干预是随机治疗分配，治疗诱导的混杂因素是治疗是否实际采取/坚持。在这一单调性假设下，我们发展了自然的直接和间接效应的有效性理论，并利用它提出了一个非参数的多重稳健估计。我们使用模拟研究演示了此估计器的有限样本属性，并将其应用于Moving to Opportunity研究的数据，以估计随机分配获得第8条住房代金券-最常见的联邦住房援助形式-对青春期男孩发展任何情绪或外在障碍的风险的自然直接和间接影响，可能通过各种学校和社区特征进行操作。
Natural direct and indirect effects are mediational estimands that decompose the average treatment effect and describe how outcomes would be affected by contrasting levels of a treatment through changes induced in mediator values (in the case of the indirect effect) or not through induced changes in the mediator values (in the case of the direct effect). Natural direct and indirect effects are not generally point‐identified in the presence of a treatment‐induced confounder; however, they may be identified if one is willing to assume monotonicity between the treatment and the treatment‐induced confounder. We argue that this assumption may be reasonable in the relatively common encouragement‐design trial setting, where the intervention is randomized treatment assignment and the treatment‐induced confounder is whether or not treatment was actually taken/adhered to. We develop efficiency theory for the natural direct and indirect effects under this monotonicity assumption, and use it to propose a nonparametric, multiply robust estimator. We demonstrate the finite sample properties of this estimator using a simulation study, and apply it to data from the Moving to Opportunity Study to estimate the natural direct and indirect effects of being randomly assigned to receive a Section 8 housing voucher—the most common form of federal housing assistance—on risk developing any mood or externalizing disorder among adolescent boys, possibly operating through various school and community characteristics.