ArXiv Pre-Print “Evaluating AI Systems under Uncertain Ground Truth: a Case Study in Dermatology” • David Stutz

In supervised machine learning, we usually assume access to ground truth label for evaluation. In many applications, however, these ground truth labels are derived from expert opinions. Disagreement among these experts is typically ignored using simple majority voting or averaging. Unfortunately, this can have severe consequences by over-estimating performance or mis-guiding model selection. In our work presented in this article, we tackle this problem by introducing a statistical framework for aggregating expert opinions.

Abstract

For safety, AI systems in health undergo thorough evaluations before deployment, validating their predictions against a ground truth that is assumed certain. However, this is actually not the case and the ground truth may be uncertain. Unfortunately, this is largely ignored in standard evaluation of AI models but can have severe consequences such as overestimating the future performance. To avoid this, we measure the effects of ground truth uncertainty, which we assume decomposes into two main components: annotation uncertainty which stems from the lack of reliable annotations, and inherent uncertainty due to limited observational information. This ground truth uncertainty is ignored when estimating the ground truth by deterministically aggregating annotations, e.g., by majority voting or averaging. In contrast, we propose a framework (cf. Figure 1) where aggregation is done using a statistical model. Specifically, we frame aggregation of annotations as posterior inference of so-called plausibilities, representing distributions over classes in a classification setting, subject to a hyper-parameter encoding annotator reliability. Based on this model, we propose a metric for measuring annotation uncertainty and provide uncertainty-adjusted metrics for performance evaluation. We present a case study applying our framework to skin condition classification from images where annotations are provided in the form of differential diagnoses. The deterministic adjudication process called inverse rank normalization (IRN) from previous work ignores ground truth uncertainty in evaluation. Instead, we present two alternative statistical models: a probabilistic version of IRN and a Plackett-Luce-based model. We find that a large portion of the dataset exhibits significant ground truth uncertainty and standard IRN-based evaluation severely over-estimates performance without providing uncertainty estimates.

Paper on ArXiv

@article{Stutz2023,
  title={Evaluating AI systems under uncertain ground truth: a case study in dermatology},
  author={David Stutz and Ali Taylan Cemgil and Abhijit Guha Roy and Tatiana Matejovicova and Melih Barsbey and Patricia Strachan and Mike Schaekermann and Jana von Freyberg and Rajeev Vijay Rikhye and Beverly Freeman and J. Perez Matos and Umesh Telang and Dale R. Webster and Yuan Liu and Greg S Corrado and Yossi Matias and Pushmeet Kohli and Yun Liu and Arnaud Doucet and Alan Karthikesalingam},
    journal={ArXiv.org},
    volume={abs/2307.02191},
    year={2023},
}