[EM] 3 or more choices - Condorcet

[Juho Laatu]

On 12.11.2012, at 17.59, Kevin Venzke wrote:

> Hi Juho,
> 
> 
>> Kevin Venzke wrote:
>>> 
>>> "Margins, it seems to me, is DOA as a proposal due to the Plurality criterion.
>>> That 35 A>B, 25 B, 40 C would elect A is too counter-intuitive."
>>> 
>>> I agree. For those who don't know, the Plurality criterion says that if  X is ranked
>>> strictly above all other candidates on more ballots than Y is ranked above any candidates,
>>> then Y must not win. 
>> 
>> 
>> Plurality criterion assumes implicit approval ("given any preference") of ranked
>> candidates (definitions above have some differences). In that sense it adds something
>> extra to pure ranking.
> 
> I don't believe the public needs to understand the terms "plurality criterion"
> or "implicit approval" or even "strategy" to find the scenario problematic.

I guess people need to understand what ranking candidates in general or ranking them above the last place means, and that such an act is supposed to mean something when they vote, if they have an opinion on the Plurality criterion (or on examples that demonstrate the impact of the Plurality criterion). Or do you mean that the Plurality criterion example would be presented and explained to the public, but assuming that they don't understand what ranking or not ranking some candidate means?

> 
> That's why I see it as such a show-stopper.
>> I wonder if the voters should be told about the Plurality criterion or if that
>> should be hidden from them (to avoid them rankig only those candidates that 
> 
>> they approve / want to promote). In some startegies that information may be 
> 
>> useful to them. But losing information because of truncation (in an election 
> 
>> that has no meaningful strategy problems) is harmful.
> Do you think that if you permit IRV voters to know that IRV satisfies
> Plurality, they will truncate more often (assuming the rules allow them 
> 
> to)?

Depends on how different properties are presented and advertised. If Plurality would be presented as an important feature of Condorcet methods, some people might take that seriously and vote accordingly (e.g. rank only those candidates that they approve). That could be relevant in IRV too, if someone would start merketing IRV using the Plurality criterion.

But in general I lean in the direction that in most cases (e.g. in Burlington) people will use ranked methods in some quite sincere way and they do not worry about the details, like IRV strategies or Plurality criterion.

However, even without stategy and property discussions, some voters may be tempted to truncate just because they get the idea (maybe from their traditional voting methods) that marking some candidate on the ballot will give him some "points". But that would be based on lack of understanding and not on the properties on the method in question. I think the correct message to voters in most ranked method based elections is to encourage them not to truncate but rank all ralevant (good and less good) candidates sincerely.

> 
> The thought that Plurality itself (satisfaction of it, or failures of it) 
> can be exploited by voters is strange to me.

Pluraity criterion can at least play a role in some strategies. Sincere rankings are 49:A, 48:B>C, 3:C>B. If the three C supporters truncate, Plurality criterion says that (former Condorcet winner) B can not win any more. Plurality criterion does not say that C must win, but if it does (as in some Condorcet methods), then those three C>B voters have a working strategy.

Also the wording and intent of Plurality criterion may lead people to think that by not ranking some candidates at all, they can decrease the chancs of those candidates to win (never mind if the voters are rational or not).

Juho



> 
> Kevin
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