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Independence of irrelevant alternatives: Difference between revisions
Independence of irrelevant alternatives (view source)
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(Ranked pairs doesn't fail this criterion.) |
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In [[voting system]]s, '''independence of irrelevant alternatives''' is the property some voting systems have that, if one option (X) wins the election, and a new alternative (Y) is added, only X or Y will win the election.
Most [[Condorcet method]]s fail this criterion, although some, such as [[Ranked Pairs]],
[[Arrow's impossibility theorem]] states that no voting system can satisfy universal domain, non-imposition, non-dictatorship, unanimity, and independence of irrelevant alternatives. In practice, this means that no deterministic ranked ballot system can satisfy independence of irrelevant alternatives without either having a dictator (whose ballot decides who wins no matter the other ballots), failing to elect a candidate that the whole electorate ranks first, or rendering one or more outcomes impossible no matter the ballots.
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