[EM] 3 or more choices - Condorcet

[Juho Laatu]

On 14.11.2012, at 2.59, Kevin Venzke wrote:

> Hi Juho,
> 
> 
> 
> ----- Mail original -----
>> De : Juho Laatu <juho4880 at yahoo.co.uk>
>>> 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?
> 
> Plurality is just a description that is convenient for discussion on the
> EM list. "Ranking above last place" isn't a concept that exists (until 
> someone feels it would aid their position to bring it up).
> 
> It just takes someone (could be an IRV advocate) to say this many voters 
> ranked this candidate first and this candidate second, and didn't rank 
> anyone else, etc. If this, without bringing up any criteria, doesn't 
> raise an awful lot of eyebrows, then I'm wrong about Plurality. But if 
> it does raise eyebrows, then it is up to the pro-margins crowd to explain 
> to the public that their mistake is that they believe in "implicit approval"
> (without having ever heard of it) and that they should stop, because it
> (you will say) encourages harmful strategy.

Ok, it seems that we are moving in the direction of marketability of the methods. All methods can be attacked based on some of their properties. And in most cases voters are quite unaware of any of those properties, until someone builds such (usually negative) marketing messages and starts using them.

Sometimes the marketing messages might be based on what actually happened in the election. In Burlington 2009 mayoral elections people were told that IRV failed to elect the Condorcet winner. But it seems that people didn't pay much attention to that failure. Sometimes the marketing stories are based just on "what might happen in theory". It may be that we are talking more about the psychology of the politicians and lobbyists here, and less about the psychology of the actual voters, or the concerns of the election method experts.

> 
> And I want note again that virtually every proposed method satisfies 
> Plurality aside from margins and MMPO. So if Plurality is the cause of 
> some harmful strategy, your offered alternative must be something really
> fantastic.

I guess Condorcet methods can't ever be successful since they fail such "terrible" criteria as "favourite betrayal" and "burial". ;-) I mean that whatever method you want to promote, there are some nasty negative marketing pitches that you must be ready to answer. I'm not sure if Plurality is the most difficult one. One reason is that even experts need to read the definition twice before they properly understand what the idea is and what the implications of the criterion might be.

> 
>>> 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.
> 
> I can't imagine that anyone would use Plurality to promote a method, 
> since even FPP satisfies it. I can only see using it to oppose a method,
> and even then it seems unnecessary to put a name to the problem.
> 
>> 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.
> 
> Ok. In the context of margins' proposability and Plurality I don't 
> actually think it matters how people would vote under it. (Though I'm sure
> it would come up. Ahaha.)
> 
>> 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.
> 
> Right. And when you advocate margins you get the job of convincing 
> everybody that they're wrong to think this way. (I do think they think 
> this way, and I don't think anyone can change it.)

Most ranked methods lose a considerable part of their benefits if people generally truncate. In the worst case the behaviour of the methods starts to resemble plurality. It is quite common that the "opposite side" will win, and then one's vote is "wasted" unless one tells which one of the "opposite side" candidates is best. I believe that many enough people will learn not to truncate, to make the results of the election meaningful and fair.

Btw, I think that in some sense margins are easy to advocate. The reason is that there is one simple answer that, if you want, can be used to answer to most attacks against Minmax(margins). The idea is roughly that you thwart all attacks on detais by repeating that the method will elect the candidate who needs least additional votes to beat all others. That is a simple and quite understandable rule that makes sense, not a complex algorithm, and any deviation from that simple rule can be presented as violation of the basic principles of the election. We may thus accept that there are some theoretical cases of burial etc., but we can say that we should still stick to the idea of electing the best candidate as defined by the "least additional votes" rule, since doing otherwise would not elect the best winner (maybe more often). Isn't that a valid marketing approach?

Margins are also a quite natural approach to measuring the strength of preference.

> 
>> 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.
> 
> I actually don't understand the meaning of this kind of statement. Who 
> is in the position of sending messages to voters? I think the political 
> players will tell their supporters whatever they think is most advantageous,
> and no one will consult the EM list.

Maybe the question of truncation will pop up in various places. I wonder who would give a general advice "yes, trunction is what you should do". That doesn't make much sense. I guess it would be more popular to say "you can rank the candidates in the new method, so be thankful about that and rank them".

It is probably easier for the politicians to say "at least I will not even rank their candidates". That is a message saying that this party/wing is so bad that I don't even want to touch them. But I guess people are used to hearing this kind of negative talk from the politicians. They might react by ignoring such recommendations, or alternatively the polarization would raise to the levels of plurality style voting between the two major wings. I hope and guess that the first approach will become more popular in time.

Juho


> 
>>> 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.
> 
> Ok.
>  
>> 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).
> 
> Ok. Though again, I see no use in bringing up this criterion except to
> oppose a method that doesn't satisfy it.
> 
> Kevin
> ----
> Election-Methods mailing list - see http://electorama.com/em for list info