13 research outputs found
Normalized Range Voting Broadly Resists Control
We study the behavior of Range Voting and Normalized Range Voting with
respect to electoral control. Electoral control encompasses attempts from an
election chair to alter the structure of an election in order to change the
outcome. We show that a voting system resists a case of control by proving that
performing that case of control is computationally infeasible. Range Voting is
a natural extension of approval voting, and Normalized Range Voting is a simple
variant which alters each vote to maximize the potential impact of each voter.
We show that Normalized Range Voting has among the largest number of control
resistances among natural voting systems
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
Range voting is resistant to control
Social choice theory is concerned with developing and evaluating voting systems, both for the use of political and organizational elections and for use as decision making process for multiagent systems. Particularly in the context of multiagent systems, computational resistance to various types of control has become a desired property of a voting system. Though manipulative actions may always be possible, strong computational barriers to efficient control can give us sufficient confidence in the integrity of an election. Range Voting is a natural extension of approval voting that is resistant to a large number of cases of control. In particular, the variant Normalized Range Voting has among the largest number of control resistances among natural voting systems
Schulze and Ranked-Pairs Voting are Fixed-Parameter Tractable to Bribe, Manipulate, and Control
Schulze and ranked-pairs elections have received much attention recently, and
the former has quickly become a quite widely used election system. For many
cases these systems have been proven resistant to bribery, control, or
manipulation, with ranked pairs being particularly praised for being NP-hard
for all three of those. Nonetheless, the present paper shows that with respect
to the number of candidates, Schulze and ranked-pairs elections are
fixed-parameter tractable to bribe, control, and manipulate: we obtain uniform,
polynomial-time algorithms whose degree does not depend on the number of
candidates. We also provide such algorithms for some weighted variants of these
problems
Attacking and defending popular election systems
Thesis (Ph. D.)--University of Rochester. Dept. of Computer Science, 2013.The thesis of this dissertation is that complexity and algorithms, used appropriately,
are important factors in assessing the value and uses of election systems. The chapter on
search versus decision points out the importance of that “appropriately”; it proves that unless
integer factoring is easy, the standard definitions of manipulability do not capture what
they were designed to capture. Other chapters use complexity and algorithms to analyze
the complexity of various types of manipulative attacks on elections, as a way of understanding
how computationally vulnerable election systems are. Among the contributions of
those chapters are: showing that a type of range voting is the most control-attack resistant
among all currently analyzed natural election systems; exploring for the first time the detailed
control complexity of Schulze elections; and exploring the parameterized complexity
of manipulative actions in Schulze and ranked-pairs elections. Such results will better allow
choosers of election methods to match the protections of the systems they choose with the
types of attack that are of greatest concern
Search versus Decision for Election Manipulation Problems
Most theoretical definitions about the complexity of manipulating elections focus on the decision problem of recognizing which instances can be successfully manipulated, rather than the search problem of finding the successful manipulative actions. Since the latter is a far more natural goal for manipulators, that definitional focus may be misguided if these two complexities can differ. Our main result is that they probably do differ: If integer factoring is hard, then for election manipulation, election bribery, and some types of election control, there are election systems for which recognizing which instances can be successfully manipulated is in polynomial time but producing the successful manipulations cannot be done in polynomial time
Search versus Decision for Election Manipulation Problems
Most theoretical definitions about the complexity of manipulating elections focus on the decision problem of recognizing which instances can be successfully manipulated, rather than the search problem of finding the successful manipulative actions. Since the latter is a far more natural goal for manipulators, that definitional focus may be misguided if these two complexities can differ. Our main result is that they probably do differ: If integer factoring is hard, then for election manipulation, election bribery, and some types of election control, there are election systems for which recognizing which instances can be successfully manipulated is in polynomial time but producing the successful manipulations cannot be done in polynomial time