Benign overfitting refers to the phenomenon where an over-parameterized model fits the training data perfectly, including noise in the data, but still generalizes well to the unseen test data.
This study focuses on understanding benign overfitting in the Out-of-Distribution (OOD) regime for over-parameterized linear models under covariate shift.
The authors provide non-asymptotic guarantees that benign overfitting occurs in standard ridge regression, even in the OOD regime under certain structural conditions of the target covariance.
Theoretical results show that Principal Component Regression (PCR) achieves a faster rate of O(1/n) for the excess risk compared to standard ridge regression's slower rate of O(1/√n) for a more general family of target covariance matrices.