Center squeeze: Difference between revisions
add link to IRV
No edit summary |
Psephomancy (talk | contribs) (add link to IRV) |
||
Line 1:
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 can be arranged on a spectrum such as "left", "center", and "right"; and of the three, the "center" candidate is the [[Condorcet winner]] or [[utilitarian winner]], but loses the election.<ref>{{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>
Most consider that if the center candidate is not too far behind in honest plurality, they should be the winner, as they would beat any other candidate in a head-to-head election, and otherwise, the voting system is encouraging strategy (typically, a favorite betrayal) from one of the other two groups.
(Note that "center" does not refer to an absolute political spectrum, but relative to the ideologies of the candidates. 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.)
Line 36:
== Prevalence ==
Voting systems
Systems
Systems
==
Some voting methods are not only vulnerable to center squeeze, but in fact, make it difficult for voters to combat the effect with strategy. [[IRV]] may be one of these: Suppose the 1st choices of the voters are 25% for the Very Liberal party, 10% for the Liberal party, and 20% for the Center party, with the rest going to the Conservative party. Putting the Center party strategically 1st in IRV risks eliminating the Liberal party, at which point their votes may go more towards the Very Liberal party, eliminating the Center party; if a liberal voter desiring consensus instead puts the Liberal party 1st, that makes it more likely the Center party will be eliminated first, and then their voters' 2nd choice may help the Liberal party eliminate the Very Liberal party, resulting in more consensus overall than if the Very Liberal party had won.
== External links ==
| |||