Robust X-Learner: Breaking the Curse of Imbalance and Heavy Tails via Robust Cross-Imputation
arXiv:2601.15360v1 Announce Type: new Abstract: Estimating Heterogeneous Treatment Effects (HTE) in industrial applications such as AdTech and healthcare presents a dual challenge: extreme class imbalance and heavy-tailed outcome distributions. While the X-Learner framework effectively addresses imbalance through cross-imputation, we demonstrate that it is fundamentally vulnerable to “Outlier Smearing” when reliant on Mean Squared Error (MSE) minimization. In this failure mode, the bias from a few extreme observations (“whales”) in the minority group is propagated to the entire majority […]