[EM] Condorcet methods - should the cycle order always determine the result order? (Toby Pereira)

[Toby Pereira]

Yes, you're right that some methods that fail independence of clones do so far more spectacularly than others. And also what you say about my example where A, B and C might be candidates of the same party but might just happen to be ranked adjacently. But I suppose that's the problem of ranked ballots - that there is no single non-arbitrary method of deciding a winner. And that is one advantage of approval/score. You would get very little disagreement about how to find the winner. That and you get a clear order with an easy-to-digest way of seeing how close it was - total approvals or score (or average score). I do think these things are worth considering in a method. For a Condorcet system, the minimax system has an advantage over most others in that you can put the finishing positions of all the candidates, as well as a meaningful number by them (the number of extra ballots required to make them a winner). Dodgson is the same, so that makes me wonder -
 which other Condorcet methods are like this? I almost think it's worth being a named criterion in its own right. Candidate result scorable or something.


>________________________________
> From: Juho Laatu <juho4880 at yahoo.co.uk>
>To: EM <election-methods at lists.electorama.com> 
>Sent: Wednesday, 5 November 2014, 22:49
>Subject: Re: [EM] Condorcet methods - should the cycle order always	determine the result order? (Toby Pereira)
>  
>
>
>One more observation on clones. I think there is a major difference between methods that systematically favour or disfavour groupings with multiple candidates (e.g. Borda where nomination of two candidates instead of one typically changes the results dramatically) and methods that can break the clone criterion in some exceptional situations. For example minmax can handle clones perfectly well if we study only those cases that do not have any loops. If we assume that loops are rare, or that they are weak if they happen to exist, also then there are no significant risks (nor benefits) if some groupings do nominate multiple candidates. I guess it is quite correct to say that in typical elections (where large number of voters make independet decisions) Borda has practical problems with clones, while minmax doesn't (although both formally violate the EM clone criterion). That difference is important when one looks for practical election methods (i.e. not
 just study theoretical properties of different methos / compliance with various formal criteria).
>
>
>Juho
>
>
>
>
>
>
>On 05 Nov 2014, at 22:54, Toby Pereira <tdp201b at yahoo.co.uk> wrote:
>
>Kemeny certainly wouldn't be my preferred choice, partly because of its lack of clone independence, but I mentioned it because it seems to come up frequently enough.
>>
>>
>>I think I remember seeing before your "done right" post. I'll have to read it again, because I remember considering the possibility of a cloneproof Borda before and deciding that any attempt to cloneproof it would leave it unrecognisable from Borda. For example, if you have the following ballots:
>>
>>
>>10: A>B>C>D>E
>>10: B>C>D>E>A
>>
>>
>>Using Borda philosophy, B is the best here, but from the perspective of A, BCDE form a clone group, so any cloneproof system would have to consider A equal to each other candidate.
>>
>>
>>I think cloneproof Condorcet systems wouldn't have a set order here. While they would rank B>C>D>E, there would be no specific place for A to go. And I think this is why (as people have said), Condorcet methods don't necessarily have a complete fixed order. For example, even though B beats C and A is equal to C, it is not the case that B beats A.
>>
>>
>>But back to Borda - if the cloneproof version of Borda uses scores (as normal Borda does), then I can't see a set of scores that would make sense here. We can have scores so that B>C>D>E. But any score for A doesn't work. Because A has to be equal to all of them!
>>
>>
>>But this also makes me wonder generally - are there any sensible cloneproof ranked-ballot systems that aren't Condorcet methods? IRV is cloneproof, but is it sensible? Is there anything else?
>    
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20141106/f108be3a/attachment-0001.htm>