Natural Language Counterfactual Explanations in Financial Text Classification

The use of large language model (LLM) classifiers in finance and other high-stakes domains calls for a high level of trustworthiness and explainability. We focus on counterfactual explanations (CE), a form of explainable AI that explains a model’s output by proposing an alternative to the original input that changes the classification. We use three types of CE generators for LLM classifiers and assess the quality of their explanations on a recent dataset consisting of central bank communications. We compare the generators using a selection of quantitative and qualitative metrics. Our findings suggest that non-expert and expert evaluators prefer CE methods that apply minimal changes; however, the methods we analyze might not handle the domain-specific vocabulary well enough to generate plausible explanations. We discuss shortcomings in the choice of evaluation metrics in the literature on text CE generators and propose refined definitions of the fluency and plausibility qualitative metrics.