Institutional Design and Differences in Roll-Call Voting Cohesion in Bicameral Legislatures: The Chilean Congress, 2006–2018

This article examines how bicameral institutional design shapes legislative cohesion in a presidential democracy. Differences in time horizon, electoral calendars and the legislative importance of bills generate systematic variation in coalition behaviour across chambers, even under similar electoral rules. Using 11,861 roll-call votes from the Chilean Congress between 2006 and 2018, we compare party coalition cohesion in both chambers using the Rice and Unity indices. Government coalitions are consistently less cohesive in the Senate than in the Chamber of Deputies, while opposition patterns vary by indicator and context. Cohesion increases for both coalitions in qualified majority votes and, to a lesser extent, in more advanced law-making stages, but absences – more frequent in the Senate – are used strategically. The Chilean case illustrates how bicameral differences in institutional design and time horizon condition legislative cohesion, with implications for the broader study of bicameralism and law-making in Latin America and beyond.