This study explores the effects of electoral rules on political polarization in the legislative branch of government. Since in Brazil the districts are also the states, and senators are chosen according to the plurality-majority rule while representatives are determined by a proportional rule, the comparison between legislative chambers enables one to test whether the plurality-majority rule induces politicians to behave less moderately, and whether the proportional rule has the opposite effect. To estimate these effects, roll call data from 1988 to 2010 was analyzed and legislators' ideal points were estimated using WNOMINATE. Evidence in favor of the hypothesis was found, although not in every circumstance.
