Strategy-free criterion: Difference between revisions
definition template
(→Commentary: modified example to make it clearer that unequal ranking in the absence of a sincere preference qualifies as falsifying) |
Psephomancy (talk | contribs) (definition template) |
||
| (5 intermediate revisions by 3 users not shown) | |||
Line 1:
The '''strategy-free criterion''' is a [[voting system criterion]] for evaluating [[voting system]]s.
== Definitions ==
Line 7 ⟶ 9:
If one candidate is preferred over each of the other candidates, that candidate is called "Condorcet candidate" or "Condorcet winner".
== Statement of
In a ranked method, it is nearly equivalent to say:
▲In a ranked method, it is nearly equivalent to say: ''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.''
▲== Complying Methods ==
*'''Complies''': [[Schulze method]] (with winning votes as the measure of defeat strength), [[MDDA]], [[MAMPO]]
Line 22 ⟶ 21:
The reader may be wondering how the Condorcet candidate, if one exists, could
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
Line 32 ⟶ 31:
In order to understand SFC, one must also understand that there are
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
Line 49 ⟶ 48:
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 also ==
*[[Voting system]]
*[[Monotonicity criterion]]
*[[Condorcet Criterion]]
*[[Generalized Condorcet criterion]]
*[[Generalized Strategy-Free criterion]]
*[[Strong Defensive Strategy criterion]]
*[[Weak Defensive Strategy criterion]]
*[[Favorite Betrayal criterion]]
*[[Participation criterion]]
*[[Summability criterion]]
== External links ==
* [http://electionmethods.org/ electionmethods.org]
{{fromwikipedia}}
[[Category:Voting system criteria]]
| |||