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Title: Mediation analysis with densities as mediators with an application to iCOMPARE trial Authors:  Jingru Zhang - University of Pennsylvania (United States) [presenting]
Haochang Shou - University of Pennsylvania (United States)
Hongzhe Li - University of Pennsylvania (United States)
Abstract: Physical activity has long been shown to be associated with biological and physiological performance and the risk of diseases. It is of great interest to assess whether the effect of an exposure or intervention on an outcome is mediated through physical activity measured by modern wearable devices such as actigraphy. However, existing methods for mediation analysis focus almost exclusively on mediation variable that is in the Euclidean space, which cannot be applied directly to the actigraphy data of physical activity. Such data is best summarized in the form of a random histogram or random density. We develop the structural equation models (SEMs) to the settings where a random density is treated as the mediator to study the indirect mediation effect of physical activity on an outcome. We provide sufficient conditions for identifying the average causal effects of a density mediator and present methods for estimating the direct and mediating effects of a density on an outcome. We apply our method to the data set from the iCOMPARE trial that compares flexible duty-hour policies and standard duty-hour policies on interns' sleep-related outcomes to explore the mediation effect of physical activity on the causal path between flexible duty-hour policies and sleep-related outcomes.