Hidden in Plain Sight: Subgroup Shifts Escape OOD Detection

Lisa M. Koch, Christian M. Schürch, Arthur Gretton, Philipp Berens

Keywords: safety, domain shift detection, subgroups, hypothesis testing, kernel methods

TL;DR: We demonstrate the limitations of OOD detection for subgroup shifts, i.e. shifts within the support of the original distribution. We show how such shifts can be detected on a population level instead and establish a baseline on histopathology images.

Abstract: The safe application of machine learning systems in healthcare relies on valid performance claims. Such claims are typically established in a clinical validation setting designed to be as close as possible to the intended use, but inadvertent domain or population shifts remain a fundamental problem. In particular, subgroups may be differently represented in the data distribution in the validation compared to the application setting. For example, algorithms trained on population cohort data spanning all age groups may be predominantly applied in elderly people. While these data are not ``out-of distribution'', changes in the prevalence of different subgroups may have considerable impact on algorithm performance or will at least render original performance claims invalid. Both are serious problems for safely deploying machine learning systems. In this paper, we demonstrate the fundamental limitations of individual example out-of-distribution detection for such scenarios, and show that subgroup shifts can be detected on a population-level instead. We formulate population-level shift detection in the framework of statistical hypothesis testing and show that recent state-of-the-art statistical tests can be effectively applied to subgroup shift detection in a synthetic scenario as well as real histopathology images.

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Paper Type: validation/application paper

Primary Subject Area: Transfer Learning and Domain Adaptation

Secondary Subject Area: Detection and Diagnosis

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Code And Data:

Code: https://github.com/lmkoch/subgroup-shift-detection
Data: https://wilds.stanford.edu/get_started/ (Camelyon17), http://yann.lecun.com/exdb/mnist/ (MNIST)