Causal Inference for Circular Data

Abstract: In causal inference, a fundamental task is to estimate the effect resulting from a specific treatment, which is often handled with inverse probability weighting. Despite an abundance of attention to the advancement of this task, most articles have focused on linear data rather than circular data, which are measured in angles. In this article, we extend the causal inference framework to accommodate circular data. Specifically, two new treatment effects, average direction treatment effect (ADTE) and average length treatment effect (ALTE), are introduced to offer a proper causal explanation for these data. As the average direction and average length describe the location and concentration of a random sample of circular data, the ADTE and ALTE measure the change in direction and length between two counterfactual outcomes. With inverse probability weighting, we propose estimators that exhibit ideal theoretical properties, which are validated by a simulation study. To illustrate the practical utility of our estimator, we analyze the effect of different job types on dispatchers' sleep patterns using data from Federal Railroad Administration.