[Election-Methods] [EM] RE : Re: Corrected "strategy in Condorcet" section

[Juho]

Forgot to say, the simulations used minmax and in usually had three  
candidates. (different voter groups sizes, e.g. 10% or less or more;  
different probabilities of ties in preferences)

Juho

On Jul 27, 2007, at 2:22 , Juho wrote:

> On Jul 23, 2007, at 17:20 , Kevin Venzke wrote:
>
>> Juho,
>>
>> --- Juho <juho4880 at yahoo.co.uk> a écrit :
>>> Margins vs. winning votes is another long term discussion topic on
>>> this list. There have been many opinions and the final conclusions
>>> may be more difficult to draw than in the Range strategy question.
>>
>> I agree here.
>>
>>> 1) It can be debated if Condorcet methods are in practice (large
>>> scale public elections) vulnerable to strategies. If not, then both
>>> margins and winning votes are safe enough and other criteria can be
>>> used to pick one of them for use.
>>
>> It's possible that a coordinated strategy may not be feasible, but
>> that
>> is not the heart of the problem in my view.
>>
>> Referring again to this scenario:
>> 49 A
>> 24 B
>> 27 C>B
>>
>> Under margins the C voters have great favorite betrayal incentive
>> without
>> any other faction having to use a coordinated strategy.
>
> Sorry about some delay in answering.
>
> There certainly are many viewpoints to this scenario. I'll present
> one. Please point out if I missed some essential things that you
> thought I should answer.
>
> In this example a single C supporter can indeed change the winner (in
> the case of margins) to B by voting B>C instead of C>B. The strategy
> is very safe since C supporters can assume that C will not win the
> race in any case.
>
> The pattern that leads to this strategic option is a loop where
> - A wins C clearly
> - C wins B with a small margin (and low number of winning votes)
> - B wins A with an even smaller margin (but high number of winning
> votes)
>
> How about the weak spots then:
> - The outcome is not that bad since there is anyway a majority that
> would elect B instead of A, and C was beaten too badly to even try to
> win (winning votes actually elect B without requiring strategic votes)
> - This scenario assumes a natural loop (not very common, and this
> type of loop maybe even less common than loops in general)
> - It is difficult to find a real world model that would lead to this
> kind of votes (what is the reason why voters voted as they did? do
> you have a story that would explain this election?)
> - Some of the strategic votes could be natural in the sense that if
> the numbers above are the outcome of an opinion poll few days before
> the election, then some C supporters might give up voting C as their
> first option since C seems to be "a sure loser"
>
> But of course the fact remains that in this scenario margins are more
> vulnerable to and encourage strategic voting. The weakest spot of
> this scenario is that it seems that it is not very likely to occur in
> real life. Maybe there are some variants with more credible "real
> life" numbers.
>
> This problem is margins specific but so far I couldn't find the
> reasons why this would make margins generally fail (worse and with
> higher probability than winning votes) in real life (large scale
> public) elections. I gave some links to the winning votes problems
> cases. They (for example) seemed more probable in real life to me
> than this scenario. But I have not done a complete enough analysis to
> claim that margins would definitely beat winning votes and that the
> probability of this scenario would be low enough not to be a threat.
>
>>> 2) There are as well cases where winning votes are more  
>>> vulnerable to
>>> strategies than margins. So the question is not one-sided.
>>
>> However, it is pretty clear that margins has a worse FBC problem than
>> WV does. Simulations have shown this, but it can be argued
>> logically as
>> well.
>
> May be so. Is there some reason why FBC would be a key criterion in
> this case? I made some time ago some simulations on margins and
> winning votes on if some certain random voter group or any of the
> voter groups could (from their point of view) improve the outcome of
> the (sincere) election by voting strategically (in whatever way). The
> simulation gave margins somewhat better results than to winning
> votes. Maybe the results depend a bit on what one simulates.
>
>> If margins outperforms WV in some respect, I'd like to be able to
>> state
>> exactly how.
>
> - to me the choices that margins make with sincere votes seem (not
> necessarily perfect for all needs but) clearly more sensible than the
> choices of winning votes
> - some of the scenarios where winning votes have strategic problems
> appear to be more probable in real life than the problem scenarios of
> margins (this feeling is however based on only a limited number of
> cases and not a thorough analysis)
> - margins are easy to explain and understand and justify to the
> voters/citizens => "least number of additional votes needed to win
> all the other candidates" (no need to talk about breaking loops and
> about complex algorithms)
>
> Sorry about not providing any more exact answers. The first
> explanation above is very obvious to me. The second case is just an
> estimate. The third one is again a fact although "social and
> psychological" by nature.
>
> I've often seen some formal properties of voting methods presented as
> final proofs of the superiority/inferiority of some particular
> method. I don't measure the benefits as number of proven theorems.
> Especially in Condorcet methods the problem cases are typically
> related to scenarios that are not very common in real life. Therefore
> I'd like to see the claims linked to real world examples that
> demonstrate the theoretical scenarios in real life situations and
> estimate their probability, harmfulness, ease of applying them, risk
> of backfiring strategies etc.
>
> Juho
>
>> Kevin Venzke
>>
>>
>>
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