[EM] 3 or more choices - Condorcet

Mon Oct 1 18:37:50 PDT 2012

To advocates of traditional (unimproved) Condorcet versions, such as
Beatpath, Ranked-Pairs, River, Kemeny, VoteFair, etc:

I'm just asking a few questions about the methods that you advocate.
Method advocates are usually willing to answer questions about their
method proposals.

In this posting, I'm not, saying that the properties that I prefer are
more important--though I've already told why I consider them to e
important. Instead, I'm merely asking what other properties are gained
in return, when the certain properties are lost. Only when people are
specific about what is gained, what the properties-tradeoff is, can
methods be meaningfully compared.

As for what's more important, that's something that you (or anyone
else) can judge, after you indicate specifically what properties are
gained by the below-listed methods, when they fail to have the
properties that I specify. When those gained properties are clearly
specified, then comparison can be made between the properties lost and
gained.

A) What is it that is gained by using traditional (unimproved)
Condorcet instead of Symmetrical Improved Condorcet?

The downsides of unimproved are:

.....1. FBC failure (though unimproved-Condorcet advocates speculate
that people won't mind)

.....2. Interpretation of equal-top and equal-bottom ranking is
contrary to the voter's preferences, intent and wishes.

Those are two drawbacks. If you advocate unimproved Condorcet, then it
must offer some advantages--important enough advantages to outweigh
the two disadvantages listed above.

B) What is it that is gained by completing Condorcet by Ranked-Pairs,
Beatpath, River, Kemeny or VoteFair, instead of just a top-count?

The downsides are:

.....1. The chicken dilemma

Most would surely agree that that is a drawback. When it can be easily
avoided by a completion by top-count, but the chicken dilemma is kept
anyway, then presumably there is something important and valuable
gained, to justify keeping the chicken dilemma. What would that be?

.....2. No obvious "normative" ("of, establishing, or proposing a
standard for a group") justification for those completions. That is, a
reason why the completion is a standard in and of itself, as opposed
to justifying it by other standards (such as strategy incentive, etc.)

Recent postings have discussed the lack of such justification for the
"strong" Condorcet completions.

By "a completion", I just mean a rule for what to do when Condorcet's
Criterion doesn't say whom to elect.

To accept these two drawbacks, something of worth must be gained by
the "strong" Condorcet completion methods. What would that be?

-------------------------------------------------

For simplicity, this posting's questions are only about the comparison
between how unimproved Condorcet does things, vs how Symmetrical ICT
does things, and the gains and losses when choosing one instead of the
other, as regards completion and the interpretation of equal top and
equal bottom ranking.

Previously, I asked Jameson similar questions about MJ's justification.

Questions like this could also be asked about the gains and losses of
properties, when choosing between unimproved Condorcet vs Approval and
Score, but I'm not doing so in this posting.

Mike Ossipoff

On Mon, Oct 1, 2012 at 6:22 PM, Juho Laatu <juho4880 at yahoo.co.uk> wrote:
> On 1.10.2012, at 19.16, Kristofer Munsterhjelm wrote:
>
>> On 10/01/2012 12:13 AM, Juho Laatu wrote:
>>> On 30.9.2012, at 15.41, Kristofer Munsterhjelm wrote:
>>
>>>> As far as intrinsically Condorcet methods go, Ranked Pairs feels
>>>> simple to me. The only tricky part is the indirect nature of the
>>>> "unless it contradicts what you already affirmed" step.
>>>
>>> To me the biggest problem of path based methods is that there is no very
>>> good real life explanation to why chains of pairwise victories are so
>>> important. In real life the idea of not electiong a candidate that would
>>> lose to someone who would lose to someone etc. doesn't sound like an
>>> important criterion (since it doesn't talk about what the candidate is
>>> like or how strong the opposition would be, but about what the set of
>>> candidates and its network of relations looks like). Probably there will
>>> never be a long chain of changes from one winner to another in real life.
>>
>> I don't think you need to go into path logic for Ranked Pairs. Rather, how about this?
>
> Ranked Pairs is based on setting up a complete ranking where the result of one candidate may depend on pairwise comparisons of some distant candidates. If therere is a large top loop, changes in opinions between A and B may change the winner from C to D. In this sense some distant opinons along the paths somewhere may influence the "goodness" of a candidate.
>
>>
>> "Because of the existence of cycles, it's obvious we need to discard some of the data. So, what data do we discard?
>
> I wouldn't say that we have to discard some data but that we may violate some pairwise preference opinions in the sense that the winner may lose some pairwise comparisons.
>
> The reason why I don't like word "discard" is actually related to the fact that this makes us too easily think of the end result as a complete ordeing of the candidates, where some facts had to be discarded because they did not fit in the picture. And here the problem is that group opinions may indeed be cyclic, and there is no need to "correct" them to a transitive order. The used words are not that important. But whatever the words, I do stick to the claim that group opinions are graphs, not linear orders, and we must decide who the winner is, in the presence of cyclic opinions (not by eliminating them, at least not in all methods).
>
> (Same comments about terms like "breaking cycles".)
>
>> If we have to discard a one-on-one victory, lets discard those that are as narrow, or involve as few voters, as possible.
>
> Yes, it is in most cases better to violate some narrow victories rather than strong ones. (We can assume full rankings and skip the "few voters" criterion since it is not essential here and it would introduce new open questions.)
>
>> Hence, we should go down the list of one-on-one contests and add the data they give to our order unless it would produce a cycle. That way, all the decisive contests get counted first and if we have to throw some away, it's the weaker ones."
>
> I can see two approaches here. One is to measure the preference relations of each candidate seprately, e.g. how much and to which other candidates someone loses and how this influences this candidate's "goodness". The other approach is that also the pairwise preferences of other unrelated candidates may influence the "goodness" of this candidate. One special case of this second approach is to say that the best winner should be picked so that the group oinion is first forced into a linear opinion using some criteria, and then the first candidate of that order is the winner. Minmax is an example in the first category where only the "personal properties" of each candidate do count.
>
>>
>> It's a little IRVish (justifying the method by the way it works rather than the outcome), but still...
>
> I think the part that was "method oriented" was the formation of the linear ordering. The way Ranked Pairs arranges the candidates is however quite intuitive and natural (not as "heuristic" and "procedural" as IRV). But as already said, the intermediate result of a linear order of the candidates is not necessary, but just a method specfic trick.
>
> Juho
>
>
>
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