Agree, Disagree, Explain: Decomposing Human Label Variation in NLI through the Lens of Explanations

Natural Language Inference datasets often exhibit human label variation. To better understand these variations, explanation-based approaches analyze the underlying reasoning behind annotators' decisions. One such approach is the LiTEx taxonomy, which categorizes free-text explanations in English into reasoning types. However, previous work applying such taxonomies has focused on within-label variation: cases where annotators agree on the final NLI label but provide different explanations. In contrast, this paper broadens the scope by examining how annotators may diverge not only in the reasoning type but also in the labeling step. We use explanations as a lens to decompose the reasoning process underlying NLI annotation and to analyze individual differences. We apply LiTEx to two NLI English datasets and align annotation variation from multiple aspects: NLI label agreement, explanation similarity, and taxonomy agreement, with an additional compounding factor of annotators' selection bias. We observe instances where annotators disagree on the label but provide highly similar explanations, suggesting that surface-level disagreement may mask underlying agreement in interpretation. Moreover, our analysis reveals individual preferences in explanation strategies and label choices. These findings highlight that agreement in reasoning types better reflects the semantic similarity of free-text explanations than label agreement alone. Our findings underscore the richness of reasoning-based explanations and the need for caution in treating labels as ground truth.