Fairness Transferability Subject to Bounded Distribution Shift
This work addresses the challenge of ensuring fairness in socially consequential tasks when deploying models in new or dynamic environments, though it is incremental as it builds on existing fairness definitions and distribution shift frameworks.
The paper tackles the problem of whether a machine learning predictor that is fair on a source distribution remains fair under bounded distribution shifts, and develops a theoretical bound to characterize this transferability, with validation on real-world data showing practical estimation of fairness violation bounds.
Given an algorithmic predictor that is "fair" on some source distribution, will it still be fair on an unknown target distribution that differs from the source within some bound? In this paper, we study the transferability of statistical group fairness for machine learning predictors (i.e., classifiers or regressors) subject to bounded distribution shifts. Such shifts may be introduced by initial training data uncertainties, user adaptation to a deployed predictor, dynamic environments, or the use of pre-trained models in new settings. Herein, we develop a bound that characterizes such transferability, flagging potentially inappropriate deployments of machine learning for socially consequential tasks. We first develop a framework for bounding violations of statistical fairness subject to distribution shift, formulating a generic upper bound for transferred fairness violations as our primary result. We then develop bounds for specific worked examples, focusing on two commonly used fairness definitions (i.e., demographic parity and equalized odds) and two classes of distribution shift (i.e., covariate shift and label shift). Finally, we compare our theoretical bounds to deterministic models of distribution shift and against real-world data, finding that we are able to estimate fairness violation bounds in practice, even when simplifying assumptions are only approximately satisfied.