Reconciling Training and Evaluation Objectives in Location Agnostic Surrogate Explainers

Matthew Clifford, Jonathan Erskine, Alexander Hepburn, Peter A. Flach, Raúl Santos-Rodríguez

Abstract: Transparency in AI models is crucial to designing, auditing, and deploying AI systems. However, 'black box' models are still used in practice for their predictive power despite their lack of transparency. This has led to a demand for post-hoc, model-agnostic surrogate explainers which provide explanations for decisions of any model by approximating its behaviour close to a query point with a surrogate model. However, it is often overlooked how the location of the query point in the decision surface of the black box model affects the faithfulness of the surrogate explainer. Here, we show that when using standard techniques, there is a decrease in agreement between the black box and the surrogate model for query points towards the edge of the test dataset and when moving away from the decision boundary. This originates from a mismatch between the data distributions used to train and evaluate surrogate explainers. We address this by leveraging knowledge about the test data distribution captured in the class labels of the black box model. By addressing this and encouraging users to take care in understanding the alignment of training and evaluation objectives, we empower them to construct more faithful surrogate explainers.