DPKM Talk: "Preventing overrepresentation when electing committees"

Oliviero Nardi 

Date/Time: 27.05.2026, 12:00 

Location: D2.2.094 

Abstract 

Committee elections are a type of election where the goal is to select a fixed number of candidates (the committee). In particular, we study committee elections with approval ballots, where each voter may approve or disapprove each candidate. This is one of the most widely studied models in social choice theory in recent years, partly because of its generality; for example, it generalises party-list parliamentary elections.

Most of the work in this area has focused on proportionality, that is, ensuring that the committee reflects the preferences of the electorate proportionally. However, almost all of this work has concentrated on a specific formulation of proportionality: if a group of voters agrees on X candidates and is large enough to deserve X seats, then it should receive at least X candidates in the final committee. In other words, the emphasis has been on preventing underrepresentation. In contrast, we study the complementary idea of preventing overrepresentation, which has received virtually no attention. This can be expressed as follows: if a group is large enough to justify at most X seats, then it should not receive more than X. We show why this is appealing, and define new voting rules and axioms (voting rule properties) that capture this principle.

This is joint work with Anton Baychkov, Martin Lackner, Jan Maly, and Jannik Peters.

Bio 

Oliviero Nardi is a fourth-year PhD student at TU Wien. His main research interest is social choice theory, in particular multi-winner elections under approval preferences.