Ideal point estimators hold the promise of identifying multiple dimensions of political disagreement as they are manifested in legislative voting. However, standard ideal point estimates do not distinguish between ideological motivations and voting inducements from parties, coalitions, or the executive. In this article we describe a general approach for hierarchically identifying an ideological dimension using an auxiliary source of data. In the case we consider, we use an anonymous survey of Brazilian legislators to identify party positions on a left-right ideology dimension. We then use this data to distinguish ideological motivations from other determinants of roll-call behavior for eight presidential-legislative periods covering more than 20 years of Brazilian politics. We find that there exists an important nonideological government-opposition dimension, with the entrance and exit of political parties from the governing coalition appearing as distinct shifts in ideal point on this second dimension. We conjecture that the Brazilian president's control over politically important resources is the source of this dimension of conflict, which has recently become far more important in explaining roll-call voting than the ideological dimension
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