[EM] Modified Bucklin
Forest Simmons
fsimmons at pcc.edu
Fri Jan 4 19:14:16 PST 2002
Here's a suggested hybrid method that completely orders the candidates
while respecting the order of the various Condorcet equivalence classes:
Seed Bubble Sort with the Modified Bucklin order described below.
[Bubble Sort recursively sorts the top m-1 seeded candidates, and then
percolates the m_th candidate as far up the list as possible by pairwise
comparisons with adjacent candidates.]
Forest
On Fri, 4 Jan 2002, Forest Simmons wrote:
> I want to make a (hopefully) final modification to my previous versions of
> Modified Bucklin. Here it is:
>
> The context is a single winner election with N candidates. Each ballot has
> (potentially) R distinguishable levels (counting truncations as the lowest
> level), some of which may go unused by some or all of the voters.
>
> For each candidate C let L be the highest level at which candidate C has
> fewer than 1/N of the ballots showing that candidate below level L.
>
> [In some cases level L will be the lowest possible level, below which
> every candidate has zero showings, which certainly represents fewer than
> 1/N of the ballots.]
>
> Also for candidate C let k be the difference in the number of ballots
> showing C above the level L and the number of ballots showing C below the
> level L.
>
> So now each candidate C has an associated ordered pair of numbers (L,k).
>
> Order the candidates according to the lexicographical order of their
> associated number pairs.
>
> This means that candidate C' is higher than C in the ordering
>
> if and only if
>
> L' is greater than L,
> OR
> L'= L AND k' > k.
>
> The highest candidate in this lexicographical order is the Modified
> Bucklin winner.
>
> This method is summable. A running sum of how many ballots each candidate
> receives in each level is possible via an N by R matrix, where N is the
> number of candidates and R is the number of possible levels.
>
> Question. Is this method consistent or even monotone?
>
> Question. Given an N by R matrix of this type computed from some set S of
> ballots, what is the smallest number of factions that a set S' (of
> Cardinal Ratings style ballots) can have while yielding the same N by R
> matrix of candidate level summaries?
>
> Forest
>
>
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