4,719 research outputs found
Manipulating Tournaments in Cup and Round Robin Competitions
In sports competitions, teams can manipulate the result by, for instance,
throwing games. We show that we can decide how to manipulate round robin and
cup competitions, two of the most popular types of sporting competitions in
polynomial time. In addition, we show that finding the minimal number of games
that need to be thrown to manipulate the result can also be determined in
polynomial time. Finally, we show that there are several different variations
of standard cup competitions where manipulation remains polynomial.Comment: Proceedings of Algorithmic Decision Theory, First International
Conference, ADT 2009, Venice, Italy, October 20-23, 200
On the Hardness of Bribery Variants in Voting with CP-Nets
We continue previous work by Mattei et al. (Mattei, N., Pini, M., Rossi, F.,
Venable, K.: Bribery in voting with CP-nets. Ann. of Math. and Artif. Intell.
pp. 1--26 (2013)) in which they study the computational complexity of bribery
schemes when voters have conditional preferences that are modeled by CP-nets.
For most of the cases they considered, they could show that the bribery problem
is solvable in polynomial time. Some cases remained open---we solve two of them
and extend the previous results to the case that voters are weighted. Moreover,
we consider negative (weighted) bribery in CP-nets, when the briber is not
allowed to pay voters to vote for his preferred candidate.Comment: improved readability; identified Cheapest Subsets to be the
enumeration variant of K.th Largest Subset, so we renamed it to K-Smallest
Subsets and point to the literatur; some more typos fixe
How Hard Is It to Control an Election by Breaking Ties?
We study the computational complexity of controlling the result of an
election by breaking ties strategically. This problem is equivalent to the
problem of deciding the winner of an election under parallel universes
tie-breaking. When the chair of the election is only asked to break ties to
choose between one of the co-winners, the problem is trivially easy. However,
in multi-round elections, we prove that it can be NP-hard for the chair to
compute how to break ties to ensure a given result. Additionally, we show that
the form of the tie-breaking function can increase the opportunities for
control. Indeed, we prove that it can be NP-hard to control an election by
breaking ties even with a two-stage voting rule.Comment: Revised and expanded version including longer proofs and additional
result
A psychologically-based model of voter turnout
We analyze a psychologically-based model of voter turnout. Potential voters experience regret if they fail to vote, which is the motivation for participation in voting. Regret from abstention is inversely related to the margin of victory. Voters on the winner's side experience less regret than those on the loser's side. We show that the unique equilibrium involves positive voter turnout. We show that the losing side has higher turnout. In addition, voter turnout is positively related to importance of the election and the competitiveness of the election. We also consider scenarios in which voters are uncertain about the composition of the electorate's political preferences and show similar phenomena emerge.voter turnout, regret, economics and psychology
Rank Aggregation Using Scoring Rules
To aggregate rankings into a social ranking, one can use scoring systems such
as Plurality, Veto, and Borda. We distinguish three types of methods: ranking
by score, ranking by repeatedly choosing a winner that we delete and rank at
the top, and ranking by repeatedly choosing a loser that we delete and rank at
the bottom. The latter method captures the frequently studied voting rules
Single Transferable Vote (aka Instant Runoff Voting), Coombs, and Baldwin. In
an experimental analysis, we show that the three types of methods produce
different rankings in practice. We also provide evidence that sequentially
selecting winners is most suitable to detect the "true" ranking of candidates.
For different rules in our classes, we then study the (parameterized)
computational complexity of deciding in which positions a given candidate can
appear in the chosen ranking. As part of our analysis, we also consider the
Winner Determination problem for STV, Coombs, and Baldwin and determine their
complexity when there are few voters or candidates.Comment: 47 pages including appendi
Vote Bying I: General Elections
We examine the consequences of vote buying, assuming this practice were al- lowed and free of stigma. Two parties compete in a binary election and may purchase votes in a sequential bidding game via up-front binding payments and/or campaign promises (platforms) that are contingent upon the outcome of the elec- tion. We analyze the role of the parties' and voters' preferences in determining the winner and the payments to voters.vote buying, political economy, campaign promises.
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