Legal Statute Identification: A Case Study using State-of-the-Art Datasets and Methods

Legal Statute Identification (LSI) involves identifying the relevant statutes (articles of law) given the facts (evidence) of a legal case. There are several key challenges in LSI, such as (i)~usage of label (statute) semantics which can be complicated and confusing; (ii)~the input text (i.e., the facts) are very long and noisy; (iii)~the label distribution usually follows a long tail, making predictions for the rare labels challenging. Although multiple methods have been proposed to address these challenges, there has not been any comprehensive study to establish the effects of these factors on different models/approaches. In this work, we reproduce several LSI models on two popular LSI datasets and study the effect of the above-mentioned challenges. We conduct thorough experiments with transformer-based encoders such as BERT and Longformer. We further try out different combinations of these encoders with approaches devised specifically for LSI, which essentially use different mechanisms to model the statute texts to enhance fact representations. Our experiments yield several interesting insights into how the above-mentioned challenges are addressed by different models, the interplay of different encoding and statute text handling measures, and how the nature of the LSI datasets affects the model performances. Finally, we also analyze the explanability capabilities of different approaches using human-annotated rationales.