User:Cymru/Independence of equivalent candidates criterion

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The Independence of Equivalent Candidates criterion was devised in 2005 by Thomas Smith. It was inspired by the inadequate definition of the independence of clones criterion which does not properly address rated voting systems and falsely presumes that correlated candidates are necessarily equivalent to each other. This criterion is a theoretical, rather than a practical criterion, and is used to describe the susceptibility of voting methods to the influence of candidates that are perceived by voters as equivalent.

Equivalent candidates are a group of candidates that are supportively ranked/rated in adjacent positions or equally ranked/rated, where equality is allowed. Thus, an approved and a disapproved candidate can never be "clones" as one is supportively rated and the other is not.

A voting method is said to be independent of equivalent candidates if the addition or removal of a equivalent candidate from a particular set of equivalent candidates in the tally, would only change the winner to another member of the set, if the original winner was a member of that set.

Methods that satisfy this criterion are approval voting, range voting, Schulze method, and Instant-runoff voting.

Independence of equivalent candidates is a weakened form of the independence of irrelevant alternatives criterion.

Binary independence condition