Robust Estimation of Causal Effects via High-Dimensional Covariate Balancing Propensity Score
This work addresses a critical issue in causal inference for researchers dealing with high-dimensional data, offering a robust estimator that is less sensitive to model misspecification, though it builds incrementally on existing covariate balancing and penalized estimation techniques.
The paper tackles the problem of estimating average treatment effects in high-dimensional observational studies where confounders may outnumber samples, proposing a robust method that achieves root-n consistency and asymptotic normality even when only one of the propensity score or outcome models is correctly specified, with simulation studies showing more accurate estimates than existing methods.
In this paper, we propose a robust method to estimate the average treatment effects in observational studies when the number of potential confounders is possibly much greater than the sample size. We first use a class of penalized M-estimators for the propensity score and outcome models. We then calibrate the initial estimate of the propensity score by balancing a carefully selected subset of covariates that are predictive of the outcome. Finally, the estimated propensity score is used to construct the inverse probability weighting estimator. We prove that the proposed estimator, which has the sample boundedness property, is root-n consistent, asymptotically normal, and semiparametrically efficient when the propensity score model is correctly specified and the outcome model is linear in covariates. More importantly, we show that our estimator remains root-n consistent and asymptotically normal so long as either the propensity score model or the outcome model is correctly specified. We provide valid confidence intervals in both cases and further extend these results to the case where the outcome model is a generalized linear model. In simulation studies, we find that the proposed methodology often estimates the average treatment effect more accurately than the existing methods. We also present an empirical application, in which we estimate the average causal effect of college attendance on adulthood political participation. Open-source software is available for implementing the proposed methodology.