Binomial voting

The binomial system (Spanish: Sistema binominal) is a voting system that was used in the legislative elections of Chile between 1989 and 2013.[1]

From an electoral system point of view, the binomial system is in effect the D'Hondt method with an open list where every constituency returns two (hence the name) representatives to the legislative body. The fact that only two candidates are elected in each district results in the peculiarity where the second majority list is overrepresented. Its use was prescribed in the respective constitutional organic law during the Pinochet regime.

The binomial system was invented in Poland in the 1980s under the Wojciech Jaruzelski regime, in order to foster political stability in the democratization process, maintaining the preeminence of the Polish United Workers' Party against the rise of the opposition movement Solidarność, being recognized as a system that promoted consensus and negotiation between opposing sides of government.[2]

The binomial system was considered by most analysts as the main constitutional lock that prevented completion of the Chilean transition to democracy.[3]