Pareto efficiency: Difference between revisions
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{{wikipedia|Pareto efficiency}}
This criterion is important in the context of [[Arrow's impossibility theorem]], since it was one of Arrow's criteria in the 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).
The Pareto criterion is the single-winner case of Hare-[[PSC]].
[[Category:Voting system criteria]]
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