causalBETA: An R Package for Bayesian Semiparametric Causal Inference with Event-Time Outcomes

Observational studies are often conducted to estimate causal effects of treatments or exposures on event-time outcomes. Since treatments are not randomized in observational studies, techniques from causal inference are required to adjust for confounding. Bayesian approaches to causal estimates are desirable because they provide 1) prior smoothing provides useful regularization of causal effect estimates, 2) flexible models that are robust to misspecification, 3) full inference (i.e. both point and uncertainty estimates) for causal estimands. However, Bayesian causal inference is difficult to implement manually and there is a lack of user-friendly software, presenting a significant barrier to wide-spread use. We address this gap by developing causalBETA (Bayesian Event Time Analysis) - an open-source R package for estimating causal effects on event-time outcomes using Bayesian semiparametric models. The package provides a familiar front-end to users, with syntax identical to existing survival analysis R packages such as survival. At the same time, it back-ends to Stan - a popular platform for Bayesian modeling and high performance statistical computing - for efficient posterior computation. To improve user experience, the package is built using customized S3 class objects and methods to facilitate visualizations and summaries of results using familiar generic functions like plot() and summary(). In this paper, we provide the methodological details of the package, a demonstration using publicly-available data, and computational guidance.