Shrinkage Bayesian Causal Forests for Heterogeneous Treatment Effects Estimation

TL;DR

This paper introduces a sparsity-enhanced Bayesian Causal Forest model that adaptively identifies relevant covariates for estimating heterogeneous treatment effects, improving performance in sparse and confounded observational data.

Contribution

It develops a novel Shrinkage Bayesian Causal Forest with priors for feature selection, allowing fully Bayesian treatment effect estimation and incorporation of prior knowledge.

Findings

Improves scalability with many covariates

Handles strongly confounded scenarios effectively

Demonstrates superior performance in simulations and real data

Abstract

This paper develops a sparsity-inducing version of Bayesian Causal Forests, a recently proposed nonparametric causal regression model that employs Bayesian Additive Regression Trees and is specifically designed to estimate heterogeneous treatment effects using observational data. The sparsity-inducing component we introduce is motivated by empirical studies where not all the available covariates are relevant, leading to different degrees of sparsity underlying the surfaces of interest in the estimation of individual treatment effects. The extended version presented in this work, which we name Shrinkage Bayesian Causal Forest, is equipped with an additional pair of priors allowing the model to adjust the weight of each covariate through the corresponding number of splits in the tree ensemble. These priors improve the model's adaptability to sparse data generating processes and allow to perform fully Bayesian feature shrinkage in a framework for treatment effects estimation, and thus to uncover the moderating factors driving heterogeneity. In addition, the method allows prior knowledge about the relevant confounding covariates and the relative magnitude of their impact on the outcome to be incorporated in the model. We illustrate the performance of our method in simulated studies, in comparison to Bayesian Causal Forest and other state-of-the-art models, to demonstrate how it scales up with an increasing number of covariates and how it handles strongly confounded scenarios. Finally, we also provide an example of application using real-world data.