Sequential pairwise elimination: Difference between revisions
Forest clarified that SPE works in reverse order of the base method. I've updated the description and example to reflect that.
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(Forest clarified that SPE works in reverse order of the base method. I've updated the description and example to reflect that.) |
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'''Sequential pairwise elimination''' is a class of voting methods devised by [[Forest Simmons]]. These methods elect from the [[Banks set]] and thus pass the [[Condorcet criterion]] and never elect covered candidates.
An SPE method, emulating legislative procedure, works by first determining a base social order by some method (e.g. [[Minmax]] or [[Range]]). Then starting with the
In effect, each candidate can be considered a proposal (a bill or an amendment). The "legislature" repeatedly votes whether to keep the current bill or to replace it with an amended bill. At the end of the procedure, the last accepted amended bill wins.
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Suppose that the base order is according to [[first past the post]]. Its order is Memphis > Nashville > Knoxville > Chattanooga.
In the first round, starting at the end of the list, we compare
In the second round, we compare
Finally, we compare Nashville to
Thus Nashville is the winner.
In this example, no matter what the order is, Nashville eventually becomes the incumbent and defeats all subsequent challengers
[[Category:Condorcet methods]]
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