[EM] Kemeny challenge

[Toby Pereira]

I don't think it is about exact clones though. First Past the Post is a bad voting system because it is not cloneproof and this shows itself with the problem of vote splitting. Voting methods that are not cloneproof suffer when there are similar candidates - they do not need to be identical.


From: Richard Fobes <ElectionMethods at VoteFair.org>
To: election-methods at electorama.com
Sent: Wednesday, 14 September 2011, 18:32
Subject: Re: [EM] Kemeny challenge

The Condorcet-Kemeny method does allow candidates to be ranked at the same preference level, and no special calculations are needed to handle these ballots.  Such "ties" can occur at any combination of preference levels.  The interactive ballots at VoteFair.org allow such "ties" and, more broadly, allow any one oval to be marked for each choice.  (On a paper-based version, if a voter marks more than one oval, only the left-most marked oval is used.)

I've addressed the "clone dependence" issue previously, yet I'll repeat the important points:  Exact clones (which is what clone dependence assumes) are very rare in real elections, and circular ambiguity (that includes the winner) is not common (because Condorcet winners are more common), so the combination of these two events -- which is what must occur in order to fail the clone independence criteria -- is extremely rare.

When I get time to reply to Warren's other message I'll address the "computational intractability" misconception.

Richard Fobes

On 9/13/2011 2:39 PM, fsimmons at pcc.edu wrote:
> The problems with Kemeny are the same as the problems with Dodgson:
> (1) computational intractability
> (2) clone dependence
> (3) they require completely ordered ballots (no truncations or equal
> ranking), so they do not readily adapt to Approval ballots, for example.
> In my posting several weeks ago under the title "Dodgson done right" I
> showed how to overcome these three problems. (The same modifications do
> the trick for both methods.) However, much of the simplicity of the
> statements of these two methods (Dodgson and Kemeny) gets lost in the
> translation.


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