Apportionment with Weighted Seats

Julian Chingoma, Ulle Endriss, Ronald de Haan, Adrian Haret, Jan Maly

Abstract: Apportionment is the task of assigning resources to entities with different entitlements in a fair manner, and specifically a manner that is as proportional as possible. The best-known application concerns the assignment of parliamentary seats to political parties based on their share in the popular vote. Here we enrich the standard model of apportionment by associating each seat with a weight that reflects the value of that seat, for example because seats come with different roles, such as chair or treasurer, that have different (objective) values. We define several apportionment methods and natural fairness requirements for this new setting, and study the extent to which our methods satisfy our requirements. Our findings show that full fairness is harder to achieve than in the standard apportionment setting. At the same time, for relaxations of those requirements we can achieve stronger results than in the more general model of weighted fair division, where the values of objects are subjective.