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Evaluating Reliability in Medical DNNs: A Critical Analysis of Feature and Confidence-Based OOD Detection

30 Aug 2024arXiv:2408.17337archive 2025-07-28

Harry Anthony, Konstantinos Kamnitsas

Reliable use of deep neural networks (DNNs) for medical image analysis requires methods to identify inputs that differ significantly from the training data, called out-of-distribution (OOD), to prevent erroneous predictions. OOD detection methods can be categorised as either confidence-based (using the model's output layer for OOD detection) or feature-based (not using the output layer). We created two new OOD benchmarks by dividing the D7P (dermatology) and BreastMNIST (ultrasound) datasets into subsets which either contain or don't contain an artefact (rulers or annotations respectively). Models were trained with artefact-free images, and images with the artefacts were used as OOD test sets. For each OOD image, we created a counterfactual by manually removing the artefact via image processing, to assess the artefact's impact on the model's predictions. We show that OOD artefacts can boost a model's softmax confidence in its predictions, due to correlations in training data among other factors. This contradicts the common assumption that OOD artefacts should lead to more uncertain outputs, an assumption on which most confidence-based methods rely. We use this to explain why feature-based methods (e.g. Mahalanobis score) typically have greater OOD detection performance than confidence-based methods (e.g. MCP). However, we also show that feature-based methods typically perform worse at distinguishing between inputs that lead to correct and incorrect predictions (for both OOD and ID data). Following from these insights, we argue that a combination of feature-based and confidence-based methods should be used within DNN pipelines to mitigate their respective weaknesses. These project's code and OOD benchmarks are available at: https://github.com/HarryAnthony/Evaluating_OOD_detection.

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apply_truncation_hook harryanthony/evaluating_ood_detection/source/methods/ReAct.py official repository ran MIT (permissive) · 5f4acd853c64f1cc · report
calculate_contribution_matrix harryanthony/evaluating_ood_detection/source/methods/DICE.py official repository ran fingerprinted MIT (permissive) · 6d387f750d46f99b · report
calculate_gram_matrices harryanthony/evaluating_ood_detection/source/methods/GRAM.py official repository ran fingerprinted MIT (permissive) · cdf914b7623c6a1b · report
create_masking_matrix harryanthony/evaluating_ood_detection/source/methods/DICE.py official repository ran fingerprinted MIT (permissive) · 7aef398e6349fd58 · report
extract_upper_triangular harryanthony/evaluating_ood_detection/source/methods/GRAM.py official repository ran fingerprinted MIT (permissive) · 5593340ed4984c72 · report
gradnorm harryanthony/evaluating_ood_detection/source/methods/gradnorm.py official repository ran MIT (permissive) · bce4f364c59dbb93 · report
modify_transforms harryanthony/evaluating_ood_detection/make_synthetic_artefacts.py official repository ran MIT (permissive) · b263e7f1e434932f · report
softmax_entropy harryanthony/evaluating_ood_detection/source/methods/entropy.py official repository ran fingerprinted MIT (permissive) · 879067ef117fce51 · report
calculate_kl_divergence harryanthony/evaluating_ood_detection/source/methods/gradnorm.py official repository unverified MIT (permissive) · a272a0afd546b8d5 · report

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Medical Image Analysis

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Softmax

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