Algorithms for Proportional Representation in Parliament in Divisor and Multiplicative Form

Abstract

We consider three algorithms for allocating parliamentary seats by proportional representation. The usual approach to describing such algorithms is to compute a quota of votes that each party uses to "acquire'' representatives. This kind of description follows a divisor method, since the number of representatives for a party is equal to the number of votes for that party, divided by the quota. We show that a simple multiplicative form with different rounding methods produces algorithms equivalent to the divisor methods. The multiplicative form is intuitive and easier to understand for a wider audience.