Strategy-free criterion: Difference between revisions
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== Definitions == |
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A [[sincere vote]] is one with no falsified preferences or preferences left unspecified when the election method allows them to be specified (in addition to the preferences already specified). |
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One candidate is preferred over another candidate if, in a one-on-one competition, more voters prefer the first candidate than prefer the other candidate. |
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If one candidate is preferred over each of the other candidates, that candidate is called "Condorcet candidate" or "Condorcet winner". |
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== Statement of Criterion == |
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''If a Condorcet candidate exists, and if a majority |
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prefers this candidate to another candidate, then the other candidate should |
prefers this candidate to another candidate, then the other candidate should |
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not win if that majority votes sincerely and no other voter falsifies |
not win if that majority votes sincerely and no other voter falsifies |
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any preferences. |
any preferences.'' |
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*'''Complies''': [[Cloneproof Schwartz Sequential Dropping]] |
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*'''Fails''': [[Approval voting]], [[Cardinal Ratings]], [[Borda count]], [[Plurality voting]], [[Instant-Runoff Voting]] |
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== Commentary == |
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The reader may be wondering how the Condorcet candidate, if one exists, could |
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possibly <em>not</em> be preferred by a majority of voters over any |
possibly <em>not</em> be preferred by a majority of voters over any |
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other candidate. The key is that some voters may have no preference |
other candidate. The key is that some voters may have no preference |
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prefer the opposite, with the other 15 having no preference between the |
prefer the opposite, with the other 15 having no preference between the |
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two. In that case, it is not true that a majority of voters prefer the |
two. In that case, it is not true that a majority of voters prefer the |
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Condorcet candidate over the other candidate, and SFC does not apply. |
Condorcet candidate over the other candidate, and SFC does not apply. |
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In order to understand SFC, one must also understand that there are |
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two types of insincere votes: false preferences and truncated |
two types of insincere votes: false preferences and truncated |
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preferences. Voters <em>truncate</em> by terminating their rank list |
preferences. Voters <em>truncate</em> by terminating their rank list |
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voter's true preferences are (A,B,C,D). The vote (A) or (A,B) would be a |
voter's true preferences are (A,B,C,D). The vote (A) or (A,B) would be a |
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truncated vote, and the vote (B,A,C) or (A,C,B) would be a falsified |
truncated vote, and the vote (B,A,C) or (A,C,B) would be a falsified |
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vote. |
vote. |
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SFC requires that the majority of voters who prefer the Condorcet candidate to |
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another particular candidate vote sincerely (neither falsify nor |
another particular candidate vote sincerely (neither falsify nor |
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truncate their preferences), and it also requires that no other voter |
truncate their preferences), and it also requires that no other voter |
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that is more likely to backfire than to succeed.) The significance of |
that is more likely to backfire than to succeed.) The significance of |
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the SFC guarantee is that the majority has no need for defensive |
the SFC guarantee is that the majority has no need for defensive |
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strategy, hence the name Strategy-Free Criterion. |
strategy, hence the name Strategy-Free Criterion. |
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[[Cloneproof Schwartz Sequential Dropping]] was shown to comply with both the |
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Condorcet and Generalized Condorcet Criteria (CC and GCC) above. |
Condorcet and Generalized Condorcet Criteria (CC and GCC) above. |
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Although compliance with CC and GCC are important, those criteria apply |
Although compliance with CC and GCC are important, those criteria apply |
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reasonable conditions, a majority of voters have no incentive to vote |
reasonable conditions, a majority of voters have no incentive to vote |
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insincerely. The fact that [[Cloneproof Schwartz Sequential Dropping]] also complies with SFC |
insincerely. The fact that [[Cloneproof Schwartz Sequential Dropping]] also complies with SFC |
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therefore enhances the significance of CC and GCC considerably. |
therefore enhances the significance of CC and GCC considerably. |
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''Some parts of this article are derived with permission from text at http://electionmethods.org'' |
''Some parts of this article are derived with permission from text at http://electionmethods.org'' |
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== See Also == |
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*[[Voting system]] |
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*[[Monotonicity criterion]] |
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*[[Condorcet Criterion]] |
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*[[Generalized Condorcet criterion]] |
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*[[Generalized Strategy-Free criterion]] |
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*[[Strong Defensive Strategy criterion]] |
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*[[Weak Defensive Strategy criterion]] |
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*[[Favorite Betrayal criterion]] |
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*[[Participation criterion]] |
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*[[Summability criterion]] |
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== External Links == |
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* [http://electionmethods.org/ Election Methods Education and Research Group] |
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{{fromwikipedia}} |
{{fromwikipedia}} |
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