[EM] 3 or more choices - Condorcet

[Juho Laatu]

On 16.11.2012, at 17.52, Kevin Venzke wrote:

> Your defense of margins (below) is apparently that the Plurality 
> failure is justified because margins makes so much sense. I don't
> know how strong that is.

One key reason behind the possible strength of sincere voting related arguments (like the "least additional votes" rule) is that if one starts to fix the strategic vulnerabilities, typically one just replaces one kind of vulnerabilities with other kind of vulnerabilities. It is thus not possible to erase them all. On the sincere performance side a good rule is more absolute. You either meet it or then you break it. From that point of view it may make sense to pick a good sincere rule and accept those (hopefully minor) vulnerabilities that will follow.

>> I guess Condorcet methods can't ever be successful since they fail such 
>> "terrible" criteria as "favourite betrayal" and 
>> "burial". ;-) 
> 
> That example doesn't make sense. At least the FBC part doesn't.

FBC has been used to market some methods as better than Condorcet. It is difficult to say how efficient that has been, but at least FBC is on the negative marketing agenda, and it has an impressive name. (also name "Plurality criterion" souds quite "essential")

>> 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 said I don't believe the criterion needs to be 
> introduced and the failure doesn't need to be explained. Only the 
> scenario itself needs to be shown in my opinion.

What is the "scenario itself"? Do you mean that one just builds an impressive negative markeing sentence (that maybe refers to the ranked candidates as approved candidates) but will not explain anything further?

>> 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.
> 
> You're writing this an example of what you would say to a skeptical 
> public?

My assumption above was that even if we would say nothing to the public, they would learn to rank sufficiently many candidates. If someone asks or the "skeptical public" gets worried, the message would be that they can quite safely rank all the candidates, and that they should give their opinion on which candidate of the other parties should win in the case that their own party can not win.

> The reason I would tell voters to truncate (or in margins' case, bury**)
> is that there is generally only risk and no possible gain to ranking the
> worst viable candidate over unviable inferior candidates. It is a 
> practical thing, not a way to overstate political sentiments.
> 
> ** - If margins elections prove to be ruined by burial then I won't 
> recommend burial.

In the election method analysis we usually take only the outcome of the current election into account when we give recommendations for strategic voting. In real ife there are also many other factors like interest to influence the next election, to influnce political life between the elections, and just to demonstrate support or non-support to certain candidates. That's why there is some tendency to vote sincerely also when that has no impact on who the winner of this election will be.

Burial is also always risky in the sense that if one makes artificially the result of some unwanted candidates better, that introduces also a risk of electing those candidates (since all candidates of a top loop are actually very strong, and it is not possible to know beforehand the sincere opinions of the voters, how opinions will change during the last days of campaigning, what other strategies there will be, and which voters are likely to vote strategically).

Juho