Double/Debiased Machine Learning for Dynamic Treatment Effects via g-Estimation
This work addresses the challenge of causal inference in dynamic settings for researchers and practitioners in fields like economics or healthcare, offering a novel extension with incremental improvements to existing methods.
The authors tackled the problem of estimating dynamic treatment effects in settings with multiple treatments over time, where treatments can affect future outcomes or states, by extending the double/debiased machine learning framework to g-estimation for dynamic treatment regimes, resulting in a method that provides finite sample guarantees, allows for non-linear effect heterogeneity, and supports high-dimensional sparse parameterizations with parametric rates for off-policy evaluation.
We consider the estimation of treatment effects in settings when multiple treatments are assigned over time and treatments can have a causal effect on future outcomes or the state of the treated unit. We propose an extension of the double/debiased machine learning framework to estimate the dynamic effects of treatments, which can be viewed as a Neyman orthogonal (locally robust) cross-fitted version of $g$-estimation in the dynamic treatment regime. Our method applies to a general class of non-linear dynamic treatment models known as Structural Nested Mean Models and allows the use of machine learning methods to control for potentially high dimensional state variables, subject to a mean square error guarantee, while still allowing parametric estimation and construction of confidence intervals for the structural parameters of interest. These structural parameters can be used for off-policy evaluation of any target dynamic policy at parametric rates, subject to semi-parametric restrictions on the data generating process. Our work is based on a recursive peeling process, typical in $g$-estimation, and formulates a strongly convex objective at each stage, which allows us to extend the $g$-estimation framework in multiple directions: i) to provide finite sample guarantees, ii) to estimate non-linear effect heterogeneity with respect to fixed unit characteristics, within arbitrary function spaces, enabling a dynamic analogue of the RLearner algorithm for heterogeneous effects, iii) to allow for high-dimensional sparse parameterizations of the target structural functions, enabling automated model selection via a recursive lasso algorithm. We also provide guarantees for data stemming from a single treated unit over a long horizon and under stationarity conditions.