Branching on the Bench: Quantifying Division in the Supreme Court with Trees

Abstract

The popular method of ideal point estimation provides empirical legal scholars with spatial representations of the Supreme Court justices that help elucidate ideological inclinations and voting behavior. This is done primarily in one dimension, where politics dominates, though recent work details a second dimension capturing differing attitudes on the authority of various legal actors. This paper introduces and explores a new network-theoretic tree-based method for visualizing the relationships between the justices, based on their voting records, that allows scholars to study the intricate branching structure of the Court. It is shown how this tool can be used to uncover periods in the Court's history where the balance on the bench fractured in unusual and interesting ways. Moreover, by defining several tree-based measures and charting their evolution over time, a picture emerges that throughout the past fifty years the Court became increasingly one-dimensional and bipolar, dividing along political lines.