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The '''center squeeze effect''' refers to a class of voting scenarios which are troublesome for many voting systems. In such a scenario, the strongest three candidates canexist bealong arranged on asome spectrum such asfrom "left", "center", andto "right";, andwith of the three, thea "center" candidate who is the [[Condorcet winner]] and/or [[utilitarian winner]], butyet who loses the election.<ref name=":0">{{Cite journal|last=Lewyn|first=Michael|date=2012|title=Two Cheers for Instant Runoff Voting|url=https://papers.ssrn.com/abstract=2276015|language=en|location=Rochester, NY|journal=6 Phoenix L. Rev.|volume=117|pages=|via=|quote=third place Candidate C is a centrist who is in fact the second choice of Candidate A’s left-wing supporters and Candidate B’s right-wing supporters. ... In such a situation, Candidate C would prevail over both Candidates A ... and B ... in a one-on-one runoff election. Yet, Candidate C would not prevail under IRV because he or she finished third and thus would be the first candidate eliminated}}</ref><ref>{{Cite journal|last=Merrill|first=Samuel|date=1984|title=A Comparison of Efficiency of Multicandidate Electoral Systems|url=http://dx.doi.org/10.2307/2110786|journal=American Journal of Political Science|volume=28|issue=1|pages=23|doi=10.2307/2110786|issn=0092-5853|quote=However, squeezed by surrounding opponents, a centrist candidate may receive few first-place votes and be eliminated under Hare.|via=}}</ref><ref>{{Cite journal|last=Merrill|first=Samuel|date=1985|title=A statistical model for Condorcet efficiency based on simulation under spatial model assumptions|url=http://dx.doi.org/10.1007/bf00127534|journal=Public Choice|volume=47|issue=2|pages=389–403|doi=10.1007/bf00127534|issn=0048-5829|quote=the 'squeeze effect' that tends to reduce Condorcet efficiency if the relative dispersion (RD) of candidates is low. This effect is particularly strong for the plurality, runoff, and Hare systems, for which the garnering of first-place votes in a large field is essential to winning|via=}}</ref>
Many consider that the Condorcet winner, or (the candidate that would beat any other candidate in a head-to-head election,) isor veryutilitarian likelywinner to(the becandidate rated most highly by the bestelectorate) candidateis the rightful winner of an election. Failing to select this candidate can encouragedencourage strategy (typically, [[Favorite betrayal criterion|favorite betrayal]]) from one of the other two groups. Note, however, that any voting method avoiding center squeeze can also incentivize strategy if one of the wings thinks they can squeeze out victory for their preferred candidate (i.e., if the "liberal"left wing" [[Bullet vote|bullet votes]] in [[Approval voting]], see [[Chicken dilemma]]).
(Note that "center" does not refer to an absolute political spectrum, but relative to the ideologies of the candidatesvoters. If the Libertarian Party holds an election, for instance, the winner should be near the center of Libertarian ideology, but if there are other candidates to either side, the most-representative candidate cannot win. This also doesn't imply any particular spectrum, such as the American left-right political spectrum; it could be any attribute on which candidates are evaluated, or multiple such attributes.<ref name=":1">{{Cite journal|last1=Davis|first1=Otto A.|last2=Hinich|first2=Melvin J.|last3=Ordeshook|first3=Peter C.|date=1970-01-01|title=An Expository Development of a Mathematical Model of the Electoral Process|url=https://semanticscholar.org/paper/66661f9678dbe956e525e87a50b5b4ee6bf280f1|journal=The American Political Science Review|volume=64|issue=2|pages=426–448|doi=10.2307/1953842|jstor=1953842|quote=Since our model is multi-dimensional, we can incorporate all criteria which we normally associate with a citizen's voting decision process — issues, style, partisan identification, and the like.|s2cid=}}</ref>)
TheWhile typically illustrated in a simple case with three candidates, the effect iscan notoccur limitedwith toany number 3of candidates: TheIn systems that suffer from center squeeze, the more candidates there are crowding the center, the less likely theya aregood representative is to win. It may eliminate not just the highest-ranked/rated candidate, but also the 2nd-highest, 3rd-highest, and so on.
== Three-candidate example ==
{{ballots|
1031: A>B>C
415: B>A>C
446: B>C>A
1108: C>B>A
}}
== Prevalence ==
Voting systems that have serious problems with center squeeze include [[First Past the Post electoral system|FPTP]], two-round [[runoff voting]], and [[IRV]].
<ref name=":0" /><ref>{{Cite journal|last=Verma|first=Dhruv|date=2021-01-01|title=Reflecting People’s Will: Evaluating elections with computer aided simulations|url=https://www.degruyter.com/document/doi/10.1515/openps-2021-0021/html|journal=Open Political Science|language=en|volume=4|issue=1|pages=228–237|doi=10.1515/openps-2021-0021|issn=2543-8042|quote=Instant runoff corrects for the spoiler effect to some extent and reduces strategic voting, however, centre squeeze is a real issue in a three legged race. With two dominant parties, it works well in that it establishes a clearer winner than plurality elections. It has however been observed that the long term end results are likely to be similar, with the same major parties and elimination of smaller parties, similar to plurality voting (but to a lesser extent) as has been witnessed in the Australian elections.}}</ref>
Systems that can do either well or poorly in a center squeeze situation include most [[graded Bucklin]] systems and [[score voting]].
3-candidate example for center squeeze under [[Condorcet]]:
{{ballots|
48: A>B
5: B
}}
When ignoring C, the votes become 52 voters preferring B to 48 preferring A. If ignoring A instead, the votes become 53 to 47 B to C. So in both directions, the center candidate is preferred by a majority, and thus is the [[Condorcet winner]].
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