Tracking Amendments to Legislation with a Novel Minimum-Edit-Distance Algorithm

Political scientists often find themselves tracking the progression of political texts; party programs, legislation or treaties. As different actors weigh in, texts change from version to version, reflecting preferences and power. But measuring how much political texts change, especially for large bodies of texts, has proven time- and resource-consuming. This paper provides a novel solution; a language-insensitive, fast minimum-edit-distance algorithm suited for political text, providing an article-by-article account of the types (insertion, deletion, substitution, transposition) and amount of changes made between text versions. Its efficiency is demonstrated by analysing EU legislative texts as they are amended over the course of negotiations. We first replicate existing studies in this field, then extend the analysis to a significantly larger number of negotiations. Results show that this automated method can reproduce the outputs of hand-coded studies with a fraction of the time and resource cost. The paper also highlights other political science applications.