Worst-Case Voting When the Stakes Are High

A. Kahng, G. Kehne
AAAI 2022
Abstract
We study the additive distortion of social choice functions in the implicit utilitarian model, and argue that it is a more appropriate metric than multiplicative distortion when an alternative that confers significant social welfare may exist (i.e., when the stakes are high). We define a randomized analog of positional scoring rules, and present a rule which is asymptotically optimal within this class as the number of alternatives increases. We then show that the instance-optimal social choice function can be efficiently computed. Next, we take a beyond-worst-case view, bounding the additive distortion of prominent voting rules as a function of the best welfare attainable in an instance. Lastly, we evaluate the additive distortion of a range of rules on real-world election data.

Experiments:

Election type Culture Candidates Voters Instances Parameters
Ordinal PrefLib [3-6] [532-1960] None https://www.preflib.org/dataset/00031
Ordinal PrefLib {13} [5199-12744] None https://www.preflib.org/dataset/00008
Ordinal PrefLib [4-9] [142-504] None https://www.preflib.org/dataset/00002
Ordinal PrefLib {5} [13318-20239] None https://www.preflib.org/dataset/00028