The senatorial election in Spain. Proportional Borda methods for selecting several candidates

Firstly, in this paper, we analyze how the electors vote in the Senate election in Spain. We show examples in which the election outcome is predictable and not proportional. We also show similar examples for other social choice problems, in which the strategic vote affords a great advantage to those who put it into practice. Secondly, we introduce the definition of a proportional social choice method. We then prove the main result that determines the only Borda type social choice method that has the same proportionality as a given divisor method.