Interpretability and Explainability: A Machine Learning Zoo Mini-tour

In this review, we examine the problem of designing interpretable and explainable machine learning models. Interpretability and explainability lie at the core of many machine learning and statistical applications in medicine, economics, law, and natural sciences. Although interpretability and explainability have escaped a clear universal definition, many techniques motivated by these properties have been developed over the recent 30 years with the focus currently shifting towards deep learning methods. In this review, we emphasise the divide between interpretability and explainability and illustrate these two different research directions with concrete examples of the state-of-the-art. The review is intended for a general machine learning audience with interest in exploring the problems of interpretation and explanation beyond logistic regression or random forest variable importance. This work is not an exhaustive literature survey, but rather a primer focusing selectively on certain lines of research which the authors found interesting or informative

REFER: An End-to-end Rationale Extraction Framework for Explanation Regularization

Human-annotated textual explanations are becoming increasingly important in Explainable Natural Language Processing. Rationale extraction aims to provide faithful (i.e., reflective of the behavior of the model) and plausible (i.e., convincing to humans) explanations by highlighting the inputs that had the largest impact on the prediction without compromising the performance of the task model. In recent works, the focus of training rationale extractors was primarily on optimizing for plausibility using human highlights, while the task model was trained on jointly optimizing for task predictive accuracy and faithfulness. We propose REFER, a framework that employs a differentiable rationale extractor that allows to back-propagate through the rationale extraction process. We analyze the impact of using human highlights during training by jointly training the task model and the rationale extractor. In our experiments, REFER yields significantly better results in terms of faithfulness, plausibility, and downstream task accuracy on both in-distribution and out-of-distribution data. On both e-SNLI and CoS-E, our best setting produces better results in terms of composite normalized relative gain than the previous baselines by 11% and 3%, respectively

Towards Faithful Model Explanation in NLP: A Survey

End-to-end neural NLP architectures are notoriously difficult to understand, which gives rise to numerous efforts towards model explainability in recent years. An essential principle of model explanation is Faithfulness, i.e., an explanation should accurately represent the reasoning process behind the model's prediction. This survey first discusses the definition and evaluation of Faithfulness, as well as its significance for explainability. We then introduce the recent advances in faithful explanation by grouping approaches into five categories: similarity methods, analysis of model-internal structures, backpropagation-based methods, counterfactual intervention, and self-explanatory models. Each category will be illustrated with its representative studies, advantages, and shortcomings. Finally, we discuss all the above methods in terms of their common virtues and limitations, and reflect on future work directions towards faithful explainability. For researchers interested in studying interpretability, this survey will offer an accessible and comprehensive overview of the area, laying the basis for further exploration. For users hoping to better understand their own models, this survey will be an introductory manual helping with choosing the most suitable explanation method(s).Comment: 62 page