Time: 1:00 pm Tuesday, 28th February 2017.
Location: SIT 459
Speaker: Haris Aziz, Data61/CSIRO and UNSW
Title: Justified Representation in Approval- Based Committee Voting
We consider approval-based committee voting, i.e. the setting where each voter approves a subset of candidates, and these votes are then used to select a fixed-size set of winners (committee). We propose a natural axiom for this setting, which we call justified representation (JR). This axiom requires that if a large enough group of voters exhibits agreement by supporting the same candidate, then at least one voter in this group has an approved candidate in the winning committee. We show that for every list of ballots it is possible to select a committee that provides JR. However, it turns out that several prominent approval-based voting rules may fail to output such a committee. We then introduce a stronger version of the JR axiom, which we call extended justified representation (EJR) that characterizes PAV — a known committee voting rule. We also consider several related questions including the complexity of associated computational problems.
(Based on joint work with Markus Brill, Vincent Conitzer, Edith Elkind, Rupert Freeman, and Toby Walsh)
Haris Aziz is a senior research scientist at Data61, CSIRO and a conjoint senior lecturer at the University of New South Wales, Sydney. His research interests lie at the intersection of artificial intelligence, theoretical computer science, and economics.