Pareto efficiency: Difference between revisions
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Virtually every devised election method satisfies this criterion. An example of a method which would fail it would be ''Random Candidate'', where some candidate is elected at random, regardless of the submitted votes. |
Virtually every devised election method satisfies this criterion. An example of a method which would fail it would be ''Random Candidate'', where some candidate is elected at random, regardless of the submitted votes. |
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A second, stronger variation of the criterion (meaning it implies the first variation of the criterion as well) is "if at least one voter prefers X over Y, and no voters prefer Y over X, then the system prefers X over Y." |
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'''Independence of Pareto-dominated alternatives (IPDA)''' says that if one option (X) wins an election, and a new alternative (Y) is added, X will win the election if Y is Pareto-dominated (using the second version of the criterion). |
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[[Category:Voting system criteria]] |
[[Category:Voting system criteria]] |
Revision as of 19:14, 12 March 2020
The Pareto criterion is a basic criterion for evaluating voting systems. It can be defined in this way:
If every voter prefers alternative X over alternative Y, then the system prefers X over Y
This criterion is important in the context of Arrow's impossibility theorem.
Virtually every devised election method satisfies this criterion. An example of a method which would fail it would be Random Candidate, where some candidate is elected at random, regardless of the submitted votes.
A second, stronger variation of the criterion (meaning it implies the first variation of the criterion as well) is "if at least one voter prefers X over Y, and no voters prefer Y over X, then the system prefers X over Y."
Independence of Pareto-dominated alternatives (IPDA) says that if one option (X) wins an election, and a new alternative (Y) is added, X will win the election if Y is Pareto-dominated (using the second version of the criterion).