Adversarial Balancing for Causal Inference.

Biases in observational data pose a major challenge to estimation methods for the effect of treatments. An important technique that accounts for these biases is reweighting samples to minimize the discrepancy between treatment groups. Inverse probability weighting, a popular weighting technique, models the conditional treatment probability given covariates. However, it is overly sensitive to model misspecification and suffers from large estimation variance. Recent methods attempt to alleviate these limitations by finding weights that minimize a selected discrepancy measure between the reweighted populations. We present a new reweighting approach that uses classification error as a measure of similarity between datasets. Our proposed framework uses bi-level optimization to alternately train a discriminator to minimize classification error, and a balancing weights generator to maximize this error. This approach borrows principles from generative adversarial networks (GANs) that aim to exploit the power of classifiers for discrepancy measure estimation. We tested our approach on several benchmarks. The results of our experiments demonstrate the effectiveness and robustness of this approach in estimating causal effects under different data generating settings.