Strategy-free criterion: Difference between revisions
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The '''strategy-free criterion''' is a [[voting system criterion]] for evaluating [[voting system]]s.
== Definitions ==
<p>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).</p>▼
▲
If one candidate is preferred over each of the other candidates, that candidate is called "Condorcet candidate" or "Condorcet winner".
== Statement of criterion ==
{{definition|If a Condorcet candidate exists, and if a majority prefers this candidate to another candidate, then the other candidate should not win if that majority votes sincerely and no other voter falsifies any preferences.}}
[[Category:Voting system criteria]]▼
In a ranked method, it is nearly equivalent to say: {{definition|If more than half of the voters rank ''x'' above ''y'', and there is no candidate ''z'' whom more than half of the voters rank above ''x'', then ''y'' must not be elected.}}
*'''Complies''': [[Schulze method]] (with winning votes as the measure of defeat strength), [[MDDA]], [[MAMPO]]
possibly
other candidate. The key is that some voters may have no preference
between a given pair of candidates. Out of 100 voters, for example, 45
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prefer the opposite, with the other 15 having no preference between the
two. In that case, it is not true that a majority of voters prefer the
Condorcet candidate over the other candidate, and SFC does not apply.
two types of insincere votes: false preferences and truncated
preferences. Voters
before their true preferences are fully specified (note that the last
choice is always implied, so leaving it out is not considered
truncation). Voters
hand, by reversing the order of their true preferences or by specifying
a preference they don't really have. Suppose, for example, that a
voter's true preferences are (A,B,C
The vote (A) or (A,B) would be a truncated vote, and the vote (B,A,C) or (A,C,B)
or (A,B,C,D,E) would be a falsified vote.
another particular candidate vote sincerely (neither falsify nor
truncate their preferences), and it also requires that no other voter
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candidate to win by truncating their preferences. (In theory, that
minority could cause the other candidate to win by falsifying their
preferences, but that would be a very risky
that is more likely to backfire than to succeed.) The significance of
the SFC guarantee is that the majority has no need for defensive
strategy, hence the name Strategy-Free Criterion.
The [[Schulze method]] was shown to comply with both the Condorcet and Generalized Condorcet Criteria (CC and GCC) above. Although compliance with CC and GCC are important, those criteria apply only in the theoretically ideal case in which all votes are sincere. The Strategy-Free criterion goes further and shows that, under certain reasonable conditions, a majority of voters have no incentive to vote insincerely. The fact that the [[Schulze method]] also complies with SFC therefore enhances the significance of CC and GCC considerably.
''Some parts of this article are derived with permission from text at http://electionmethods.org''
== See
*[[Voting system]]
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*[[Summability criterion]]
== External
* [http://electionmethods.org/ Election Methods Education and Research Group]▼
{{fromwikipedia}}
▲[[Category:Voting system criteria]]
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