Causal Effect Estimation on Hierarchical Spatial Graph Data

Estimating individual treatment effects from observational data is a fundamental problem in causal inference. To accurately estimate treatment effects in the spatial domain, we need to address certain aspects such as how to use the spatial coordinates of covariates and treatments and how the covariates and the treatments interact spatially. We introduce a new problem of predicting treatment effects on time series outcomes from spatial graph data with a hierarchical structure. To address this problem, we propose a spatial intervention neural network (SINet) that leverages the hierarchical structure of spatial graphs to learn a rich representation of the covariates and the treatments and exploits this representation to predict a time series of treatment outcome. Using a multi-agent simulator, we synthesized a crowd movement guidance dataset and conduct experiments to estimate the conditional average treatment effect, where we considered the initial locations of the crowds as covariates, route guidance as a treatment, and number of agents reaching a goal at each time stamp as the outcome. We employed state-of-the-art spatio-temporal graph neural networks and neural network-based causal inference methods as baselines, and show that our proposed method outperformed baselines both quantitatively and qualitatively.