Title: When Measurement Mediates the Effect of Interest Show Chinese title

Title: 当测量中介感兴趣的效果时

Abstract: Many health promotion strategies aim to improve reach into the target population and outcomes among those reached. For example, an HIV prevention strategy could expand the reach of risk screening and the delivery of biomedical prevention to persons with HIV risk. This setting creates a complex missing data problem: the strategy improves health outcomes directly and indirectly through expanded reach, while outcomes are only measured among those reached. To formally define the total causal effect in such settings, we use Counterfactual Strata Effects: causal estimands where the outcome is only relevant for a group whose membership is subject to missingness and/or impacted by the exposure. To identify and estimate the corresponding statistical estimand, we propose a novel extension of Two-Stage targeted minimum loss-based estimation (TMLE). Simulations demonstrate the practical performance of our approach as well as the limitations of existing approaches. Show Chinese abstract

Abstract: 许多健康促进策略旨在扩大目标人群的覆盖范围，并改善被覆盖人群的健康结局。 例如，一项HIV预防策略可以扩展对具有HIV风险人群的风险筛查以及生物医学预防措施的提供。 这种情境下会产生一个复杂的缺失数据问题：该策略通过扩大覆盖范围直接和间接地改善健康结局，但结局仅在被覆盖人群中进行测量。 为了正式定义此类情境下的总因果效应，我们使用了**反事实层效果**：即结局仅对那些因缺失性或暴露影响而使成员资格受到影响的群体有意义的因果估计量。 为识别并估计相应的统计估计量，我们提出了两阶段目标最小损失估计（TMLE）的一种新扩展方法。 模拟研究表明了我们方法的实际表现以及现有方法的局限性。