Favorite betrayal criterion
In social choice theory, the Favorite Betrayal criterion is a criterion for evaluating voting systems.
Definition
A voter optimizes the outcome (from his own perspective) if his vote causes the election of the best possible candidate that can be elected, based on his own preferences, given all the votes cast by other voters.
Statement of the criterion
For any voter who has a unique favorite, there should be no possible set of votes cast by the other voters such that the voter can optimize the outcome (from his own perspective) only by voting someone over his favorite.
Complying methods
The approval method complies with the favorite betrayal criterion, while cardinal ratings, Borda count, plurality voting, and instant-runoff voting do not comply. It is not known whether Cloneproof Schwartz Sequential Dropping complies. One form of majority-choice approval does not comply, the other form does.
Commentary
Election methods that meet this criterion provide no incentive for voters to betray their favorite candidate by voting another candidate over him or her.
Some parts of this article are derived with permission from text at http://electionmethods.org