Overrepresentation Axioms in Multi-Winner Voting

Speaker(s)

Anton Baychkov

Affiliation

University of Warwick

Language of the talk

English

Date

Oct. 8, 2026, 12:15 p.m.

Room

room 4060

Seminar

Seminar Algorithmic Economics

In the recent social choice literature on proportional representation, much attention has been given to the question of avoiding underrepresentation in approval-based multi-winner voting. In our work, we explore the largely overlooked complementary question of avoiding overrepresentation. Intuitively, overrepresentation happens when a group determines a disproportionately large part of the committee, thereby exceeding the group’s quota.

We formulate a strong and appealing axiom for avoiding overrepresentation, called justified upper quota (JUQ). We investigate whether (exhaustive) outcomes satisfying JUQ can be achieved and the extent to which JUQ is compatible with lower quota notions. However, JUQ is incompatible with several normative proportionality notions studied in the literature, including priceability and laminar proportionality. In our ongoing work, we investigate a different upper quota axiom that is compatible with these notions.

This talk is based on our published paper https://arxiv.org/abs/2606.19968, as well as unpublished, ongoing work.