The Impact of Split Classifiers on Group Fairness


Hao Wang, Hsiang Hsu, Mario Diaz, and Flavio P. Calmon. 2021. “The Impact of Split Classifiers on Group Fairness.” In IEEE International Symposium on Information Theory (ISIT).
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Disparate treatment occurs when a machine learning model produces different decisions for groups of individuals based on a sensitive attribute (e.g., age, sex). In domains where prediction accuracy is paramount, it could potentially be acceptable to fit a model which exhibits disparate treatment. To evaluate the effect of disparate treatment, we compare the performance of split classifiers (i.e., classifiers trained and deployed separately on each group) with group-blind classifiers (i.e., classifiers which do not use a sensitive attribute). We introduce the benefit-of-splitting for quantifying the performance improvement by splitting classifiers when the underlying data distribution is known. Computing the benefit-of-splitting directly from its definition involves solving optimization problems over an infinite-dimensional functional space. Under different performance measures, we (i) prove an equivalent expression for the benefit-of-splitting which can be efficiently computed by solving small-scale convex programs; (ii) provide sharp upper and lower bounds for the benefit-of-splitting which reveal precise conditions where a group-blind classifier will always suffer from a non-trivial performance gap from the split classifiers.