Coalition incentives and party bias in Chile

Abstract

This article revisits the debate over Chile's binomial electoral rules and its consequences and examines how the new electoral system conceived by a democratic congress altered political competition. It utilizes a seat-vote model of multiparty competition to analyze party bias under the binomial rule. This approach differs substantively from prior studies of the Chilean case that focused primarily on the disproportionality of aggregate results. In contrast to earlier analyses, the findings reveal that the allocation of the seats under the binominal resulted in significant party bias benefiting the main parties of the right. This bias, however, was eliminated after the electoral reform. The new rule continues to provide majoritarian benefits to parties receiving larger shares of votes, but this effect is less pronounced than before. It is now easier for small parties to gain seats, which has increased party fragmentation. However, we show that coalition incentives, which were heralded as one of the main advantages of the binomial rule, are also significant under the new rule in use since 2017.