Gibbard-Satterthwaite theorem: Difference between revisions
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The '''Gibbard-Satterthwaite theorem''' states that every unimposing [[voting system]] (one in which every preference order is achievable) which chooses between three or more candidates, must be either dictatorial or manipulable (i.e. susceptible to [[tactical voting]]). It follows from [[Arrow's impossibility theorem]].
==Statement==
For every voting rule, one of the following three things must hold:
# The rule is dictatorial, i.e. there exists a distinguished voter who can choose the winner
# The rule limits the possible outcomes to only two alternatives
# The rule is susceptible to [[strategic voting]]: some voter's sincere ballot may not defend their opinion best.
[[Category:Voting theory]]
[[Category:Voting system criteria]]
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