Label-free estimation of clinically relevant performance metrics under distribution shifts

TL;DR

This paper introduces methods to estimate full confusion matrices for medical image classifiers without labels, evaluates them on chest X-ray data under distribution shifts, and highlights their reliability and limitations in clinical settings.

Contribution

It generalizes existing performance prediction methods to estimate full confusion matrices and benchmarks their effectiveness on real-world and simulated distribution shifts in medical imaging.

Findings

Confusion matrix estimation reliably predicts clinical metrics under shifts.

Current methods have failure modes revealed by simulated shifts.

Performance monitoring techniques need better understanding for clinical deployment.

Abstract

Performance monitoring is essential for safe clinical deployment of image classification models. However, because ground-truth labels are typically unavailable in the target dataset, direct assessment of real-world model performance is infeasible. State-of-the-art performance estimation methods address this by leveraging confidence scores to estimate the target accuracy. Despite being a promising direction, the established methods mainly estimate the model's accuracy and are rarely evaluated in a clinical domain, where strong class imbalances and dataset shifts are common. Our contributions are twofold: First, we introduce generalisations of existing performance prediction methods that directly estimate the full confusion matrix. Then, we benchmark their performance on chest x-ray data in real-world distribution shifts as well as simulated covariate and prevalence shifts. The proposed confusion matrix estimation methods reliably predicted clinically relevant counting metrics on medical images under distribution shifts. However, our simulated shift scenarios exposed important failure modes of current performance estimation techniques, calling for a better understanding of real-world deployment contexts when implementing these performance monitoring techniques for postmarket surveillance of medical AI models.