Making Votes Talk: Ideology and Government Influence on Legislative Behavior

Abstract

In this paper we propose a variation on the standard item response model to allow for the incorporation of ideology survey data into the estimation of legislator ideal points from roll calls. We estimate the model for 20 years of data from Brazil, where the existence of an extreme multiparty system provides empirical leverage to distinguish between different motivations of politicians, which is not generally possible in the two party US system where ideology and party membership are highly collinear. Our model shows that there exists a second non-ideological government-opposition dimension, which at times can be shown to be more important than the standard ideological dimension. We conjecture that the president's greater control over politically important resources is the source of this second dimension of conflict.