[EM] Scoring (was Re: OpenSTV 2.1.0 released)

[Juho Laatu]

I will not comment the Dodgson and changing vs. adding votes related misunderstandings. I hope that misunderstanding is now solved. My example best sincere winner criterion was meant to refer to the Minmax(margins) philosophy.

On 24.9.2012, at 16.33, Michael Ossipoff wrote:

> If you think that
> MinMax(margins) or Dodgson is better than Symmetrical ICT, under
> sincere voting, you have yet to tell why.

My comments applied to any definition of best sincere winner. I didn't comment on which one is best. (Instead I said that different elections and different people may have different targets.) I noted at some point that SITC has some strategy defence related properties that may make it an unlikely choice as a best sincere winner criterion.

> Do you really think that would help hir
> status against opposition in office better than being the most
> favorite candidate in the top cycle?

I don't know what "most favorite" means here. Minmax(margins) can elect outside the top cycle if such a candidate is closest to being a CW (measured in number of required additional votes). I don't claim that this criterion would be the best one for all elections, but it is one that sounds usable for some needs.

> So you're saying that different voting systems should be used for
> different elections. But, as each new election comes near, who decides
> which method will be used for that particular election?

I'd expect one series of elections to stick to one method (and be based on one stable understanding on what kind of a candidate is the best sincere winner).

> Should we use different voting systems for presidential and
> Congressional elections? If so, then which one would be better (by
> ideal sincere winner) for the presidency,and which would be better for
> Congress?

Those two elecions are very different by nature, and therefore they could well have different targets / understanding of whom to elect with sincere votes. The question on which method and which sincere winner criterion to choose is very difficlt since changes to the current system may mean changes to the very basic concepts of the system. There are multiple options. One interesting question is if the president shoud be from a large party of if he/she could be a compromise candidate that has no major party behind him/her. In the Congress one has to decide e.g. if one wants to keep the two-party approach or not. The end result might be two very different election methods.

> Of course, judging by how well they choose the ideal sincere winner
> assumes that you still think that there won't be a chicken dilemma,
> and can tell why.

I see the sincere winner criterion and strategic concerns as two separate topics. The method that will be eventually used may deviate from what the sincere winner criterion points to if there are strategic concerns that must be addressed by selecting a method that has the required strategy related properties.

> If there will be defection in situations like the chicken
> dilemma examples, then can you still advocate Beatpath,
> MinMax(margins) or Dodgson over SITC, by saying they will get sincere
> rankings?

You have to pick the method so that strategic concerns will be properly adressed. I don't want to take position if one of those is absolutely better than others (since that is not relevant to my claim).

>> I tried to cover all the questions in your mail. You may point out the unanswered ones, so I can check what I can do with them.

I don't think the following four questions that you gave as a response are ones that I left unanswered, but new questions or new formulations. I'l check them anyway.

> 1. What makes you think that MinMax(margins), Dodgson, or Beatpath
> won't have a chicken dilemma?

I already said that I do believe that basic Condorcet methods are not very prone to this problem. I know that you disagree. Maybe you'll find one day a proof that will convince me.

> Must I do that, to show you their
> chicken dilemma? Request it and I will.

No need since I don't expect that to change my opinions. It could be a wasted effort. I'm interested if there is something really convincing, but maybe better leave this topic this time, with the assumption that I would not believe it anyway.

> 2. What makes you so sure that the United States won't have a
> significant amount of favorite-burial, when unimproved Condorcet, such
> as Dodgson, MinMax(margins) or Beatpath, is used?

I'm not "sure" but my best guess is that basic Condorcet methods would work well enough. My confidence is based on theoretical studies, experiences with Condorcet in non-political elections and experiences with IRV in political elections (also in the U.S.). Many Condorcet startegies are difficult to identify, to use, to coordinate, and often they may also backfire. The details have been debated numerous times in the history on the EM list.

> Sometimes you seem to say that you're just speaking in general, about
> most societies, or many societies. Sometimes, though, you make
> assertions about what won't happen here.

I started with general claims but I commented also the U.S. realted stuff since that seems to be on your agenda.

> 3. What is your best argument to support your belief that Dodgson,
> MinMax(margins) or Beatpath would do better at choosing the ideal
> sincere winner, if voting were sincere, than SITC would do?

I don't claim that. I left the selection of the sincere winner criterion open. As already noted, methods that are strongly strategy defence related may not be exactly built to reflect targets that have been set for selecting the winner based on sincere votes. SITC may be seen to fall in this category (and others too, like winning votes based Beatpath).

> 4. Tell the requirements that describe the ideal sincere winner.

I repeat, I left the selection of the sincere winner criterion flexible and open. I presented one example definition that could be used somewhere.

If you want some more generic comments, I might say that a good ideal sincere winner definition is supposed to tell what kind of properties the society wants the winner to have. It does not care about strategic vulnerabilities and does not defend against them. You could want the winner to be a person that is accepted by all, supported by majority, one that has strong support of some major party, one that has wide geographical support, support in all age groups, one that is not hated by any state, or whatever that makes the winner good. Once you know what you want, you can pick a practical election method that elects such a candidate (or is close enough), maybe tries to defend against strategies, is simple enough to use etc.

> Certainly SITC is a different method from Dodgson or MinMax(margins).
> It wasn't clear that that's what you meant. But, if that's what you
> meant, then you're right about that.
> 
> So what?

That was part of my basic claim that best winner criteria and methods that aim at being strategy proof are different. You seem to be close to saying that SITC is not only a realtively strategy resistant method but also (close to) your definition of an ideal winner with sincere votes.

> You mean the status against opposition in office of the candidate
> whose largest margin against him, in favor of another candidate, is
> the least. And being the most favorite, having the largest faction,
> doesn't confer any status against opposition in office? :-)

Yes, the "least additional support/votes required" criterion (as a definition of good sincere winner) points in that direction. I don't know what "most favorite" and "largest faction" exactly mean, but I think they are not addressed by the "least additional support/votes required" criterion. It is characteristic to Condorcet methods (like Minmax(margins)) that they can sometimes elect compromise candidates that have limited first preference support.

Juho