District magnitude, electoral coordination, and legislative fragmentation

ABSTRACT Theories of party systems suggest that more restrictive rules should lead to fewer parties. According to this line of reasoning, parties and voters should strategically respond to reforms in electoral rules, such as changes in district magnitude. That is, a decrease in district magnitude should decrease the size of the party system, whereas an increase in magnitude should enlarge the party system. Using a series of difference-in-differences models based on data from Brazilian municipalities before and after an exogenous reform in magnitude, I study the effects of this electoral reform on both electoral coordination and legislative fragmentation. Contrary to the expectation, the number of lists did not change after a decrease in magnitude. However, parties formed more pre-electoral coalitions in municipalities that lost seats. Voters also coalesced around fewer lists. Lastly, as expected, the reform produced a decrease in legislative fragmentation. Both mechanical and psychological effects were responsible for this modification in fragmentation.