Voting power of political parties in the Senate of Chile during the whole binomial system period: 1990-2017

The binomial system is an electoral system unique in the world. It was used to elect the senators and deputies of Chile during 27 years, from the return of democracy in 1990 until 2017. In this paper we study the real voting power of the different political parties in the Senate of Chile during the whole binomial period. We not only consider the different legislative periods, but also any party changes between one period and the next. The real voting power is measured by considering power indices from cooperative game theory, which are based on the capability of the political parties to form winning coalitions. With this approach, we can do an analysis that goes beyond the simple count of parliamentary seats.