42,825 research outputs found
Heuristics in Multi-Winner Approval Voting
In many real world situations, collective decisions are made using voting.
Moreover, scenarios such as committee or board elections require voting rules
that return multiple winners. In multi-winner approval voting (AV), an agent
may vote for as many candidates as they wish. Winners are chosen by tallying up
the votes and choosing the top- candidates receiving the most votes. An
agent may manipulate the vote to achieve a better outcome by voting in a way
that does not reflect their true preferences. In complex and uncertain
situations, agents may use heuristics to strategize, instead of incurring the
additional effort required to compute the manipulation which most favors them.
In this paper, we examine voting behavior in multi-winner approval voting
scenarios with complete information. We show that people generally manipulate
their vote to obtain a better outcome, but often do not identify the optimal
manipulation. Instead, voters tend to prioritize the candidates with the
highest utilities. Using simulations, we demonstrate the effectiveness of these
heuristics in situations where agents only have access to partial information
Polls, Coalition Signals, and Strategic Voting: An Experimental Investigation of Perceptions and Effects
The paper investigates how poll information and coalition signals affect strategic voting, defined as casting a vote for a party other than the most preferred party to better influence the election outcome. In particular if the outcome of an election is perceived to be close, voters in multi-party systems with proportional representation and coalition governments should have an incentive to cast a vote for the party that best influences the formation of the next government. The study focuses in particular on voters’ attention to and perception of polls and coalition signals sent by parties before elections. The study used an innovative design that embedded a laboratory experiment in two real election campaigns, allowing the manipulation of poll results and coalition signals in a realistic environment. The findings suggest that political sophistication plays a crucial role for the accurate perception of polls and strategic voting. Coalition signals are found to have a surprisingly strong effect on (apparently) strategic voting.
The Complexity of Online Manipulation of Sequential Elections
Most work on manipulation assumes that all preferences are known to the
manipulators. However, in many settings elections are open and sequential, and
manipulators may know the already cast votes but may not know the future votes.
We introduce a framework, in which manipulators can see the past votes but not
the future ones, to model online coalitional manipulation of sequential
elections, and we show that in this setting manipulation can be extremely
complex even for election systems with simple winner problems. Yet we also show
that for some of the most important election systems such manipulation is
simple in certain settings. This suggests that when using sequential voting,
one should pay great attention to the details of the setting in choosing one's
voting rule. Among the highlights of our classifications are: We show that,
depending on the size of the manipulative coalition, the online manipulation
problem can be complete for each level of the polynomial hierarchy or even for
PSPACE. We obtain the most dramatic contrast to date between the
nonunique-winner and unique-winner models: Online weighted manipulation for
plurality is in P in the nonunique-winner model, yet is coNP-hard (constructive
case) and NP-hard (destructive case) in the unique-winner model. And we obtain
what to the best of our knowledge are the first P^NP[1]-completeness and
P^NP-completeness results in the field of computational social choice, in
particular proving such completeness for, respectively, the complexity of
3-candidate and 4-candidate (and unlimited-candidate) online weighted coalition
manipulation of veto elections.Comment: 24 page
Manipulation and Control Complexity of Schulze Voting
Schulze voting is a recently introduced voting system enjoying unusual
popularity and a high degree of real-world use, with users including the
Wikimedia foundation, several branches of the Pirate Party, and MTV. It is a
Condorcet voting system that determines the winners of an election using
information about paths in a graph representation of the election. We resolve
the complexity of many electoral control cases for Schulze voting. We find that
it falls short of the best known voting systems in terms of control resistance,
demonstrating vulnerabilities of concern to some prospective users of the
system
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