Symmetrical ICT: Difference between revisions
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'''Symmetrical ICT''', short for '''Symmetrical Improved Condorcet, Top''' is a voting method designed by [[Mike Ossipoff|Michael Ossipoff]]. <!-- when? link to EM? --> It is based on Kevin Venzke's concept of "Improved Condorcet", which is a modification of pairwise comparison logic that enables methods to pass the [[favorite betrayal criterion]] at the cost of sometimes failing the [[Condorcet criterion]]. |
'''Symmetrical ICT''', short for '''Symmetrical Improved Condorcet, Top''' is a voting method designed by [[Mike Ossipoff|Michael Ossipoff]]. <!-- when? link to EM? --> It is based on Kevin Venzke's concept of "Improved Condorcet", which is a modification of pairwise comparison logic that enables methods to pass the [[favorite betrayal criterion]] at the cost of sometimes failing the [[Condorcet criterion]]. |
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However, Symmetrical ICT doesn't actually pass the [[favorite betrayal criterion]]. |
However, Symmetrical ICT doesn't actually pass the [[favorite betrayal criterion]] (as shown below). |
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==Definition== |
==Definition== |
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== Improved Condorcet == |
== Improved Condorcet == |
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Condorcet methods usually have a low but nonzero rate of [[favorite betrayal]] failures.<ref>{{cite web|url=http://lists.electorama.com/pipermail/election-methods-electorama.com/2005-June/114476.html|title=Measuring the risk of strict ranking|website=Election-methods mailing list archives|date=2005-06-28|last=Venzke|first=K.}}</ref> |
Condorcet methods usually have a low but nonzero rate of [[favorite betrayal]] failures.<ref>{{cite web|url=http://lists.electorama.com/pipermail/election-methods-electorama.com/2005-June/114476.html|title=Measuring the risk of strict ranking|website=Election-methods mailing list archives|date=2005-06-28|last=Venzke|first=K.}}</ref> '''Improved Condorcet''' is a modification of pairwise comparisons in an otherwise Condorcet-compliant method to turn absolute Condorcet compliance and a low rate of [[FBC]] failure into absolute FBC compliance and a low rate of [[Condorcet criterion]] failures (along with absolute Majority Condorcet compliance). |
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Mike Ossipoff argued that improved Condorcet allows a voter who wants one of X and Y to win, and who ranks X first, to change a ranking of X>Y into X=Y without undue risk that this will change the winner from Y to someone lower ranked by that voter; and thus that it's better to satisfy the IC version of Condorcet than the actual [[Condorcet criterion]]. |
Mike Ossipoff argued that improved Condorcet allows a voter who wants one of X and Y to win, and who ranks X first, to change a ranking of X>Y into X=Y without undue risk that this will change the winner from Y to someone lower ranked by that voter; and thus that it's better to satisfy the IC version of Condorcet than the actual [[Condorcet criterion]]. |
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It was intended to pass the [[favorite betrayal criterion]], but doesn't succeed in doing so due to the "(X>Y) > (Y>X)" term in the definition. It is possible that a voter can lower their favorite from the top and thereby make their compromise the only candidate who isn't "beaten." |
It was intended to pass the [[favorite betrayal criterion]], but doesn't succeed in doing so due to the "(X>Y) > (Y>X)" term in the definition. It is possible that a voter can lower their favorite from the top and thereby make their compromise the only candidate who isn't "beaten." |
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=== Favorite betrayal example === |
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0.389: B>A=C |
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0.290: A>C>B |
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0.241: C>B>A |
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0.079: A≥C>B ⇒ C>A=B |
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In this case, the voters on the bottom row can elect a better candidate, C, by reversing their preference for A. |
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==Notes== |
==Notes== |
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