Measuring party loyalty

Abstract Measuring party loyalty (and party effects, more broadly) in roll call voting has long been a contentious matter in the study of legislative behavior. While techniques for measurement in this arena are numerous, most of them suffer from a fatal flaw: they improperly (or insufficiently) separate measures of preferences from party effects. A significant part of this measurement challenge is the identification of (a) which roll calls leaders care about and (b) in which direction they desire their members to vote. In this paper, we use a novel dataset of party leader speeches from the 101st to 113th Congresses to develop a model of party loyalty and measure loyalty across members and time. Unlike existing techniques, we allow for party influence to vary across legislators and time. Additionally, our model provides estimates of legislator ideology and party loyalty disentangled from one another. Using these estimates, we explore the dynamics of loyalty in the contemporary Congress and unearth findings quite different from extant measures in the literature.