[EM] Condorcet-Kemeny calculations are not NP-hard

[Toby Pereira]

From: Richard Fobes <ElectionMethods at VoteFair.org>
To: election-methods at electorama.com
Sent: Thursday, 29 September 2011, 8:43
Subject: [EM] Condorcet-Kemeny calculations are not NP-hard


This is very cryptic. What is this named advantage and why haven't you named it here? Is the unnamed advantage also indescribable?

>The only valid disadvantage is that in very rare cases it fails the "independence of clones" criteria, yet this perceived disadvantage does not yield unfair results if all aspects of >VoteFair Ranking are used.

I'm not sure how rare it would be myself (an exact clone isn't required for a non-cloneproof method to have problems). So VoteFair doesn't use the Kemeny method then?

But having said that, failing independence of clones seems to me to be just one aspect of failing independence of irrelevant alternatives, which all Condorcet methods fail. So, for example, the Schulze method might not have problems when there are clones in the Smith Set, but it might have problems caused by a candidate introduced to have specific properties relative to the other candidates in the Smith Set. The Kemeny-Young method might (just speculating) not suffer as badly with this candidate. It's just that among the umbrella of irrelevant alternatives, clones have specifically been given their own criterion. You could probably make up other more obscure criteria under this umbrella but that cause just as many problems.
>Some people have questioned why it is worth doing Condorcet-Kemeny calculations when there are faster Condorcet methods.  The answer is that Condorcet-Kemeny >results offer lots of advantages, including one named advantage that is currently underappreciated and a significant advantage that has not yet been named or widely >recognized. 
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