[EM] SODA might be the method we've been looking for.

[Andy Jennings]

Jameson,

Believe me, I'm on board with SODA.  I think I, too, like it better than
LRV, but I'm still trying to get a handle on LRV to make sure.

In my opinion (and my wording), SODA's advantages are:

1. The laziest possible voter, who just bullet votes for his favorite, is
still casting a (nearly?) optimal vote that is fair to him and to the rest
of society.

2. Voters can vote approval style, instead, if they want.

3. The only people who have to rank all the candidates are the candidates
themselves, who should be willing to do the work to come up with a full
honest ranking.  Their ratings are public, so we can call them out if they
try to use turkey-raising or other dishonest strategies.

4. There is a "delegation" phase after the election where the candidates
can negotiate an outcome, but their ability to negotiate back-room deals is
severely limited because they have to use their pre-declared rankings and
they have to play in an order determined by the votes.  In fact, there will
be a game-theory dominant equilibrium and the candidates will probably have
very little power to change the outcome.  Chicken scenarios are avoided
because they know the play order, the other candidates' rankings, and
exactly how much voting weight each one has.

5. If there is some super-weak Condorcet winner that is totally unfit to
govern, then the others can indeed block him in the delegation phase.

I don't see any huge theoretical downsides.  Do others still have
reservations about SODA?  I realize that some people may be opposed to
delegation, in principle.  And others think delegable systems just don't
have a chance of getting implemented.  So I think these debates about which
is the best voting system in the standard (non-delegable) model are still
useful.  I also think it's useful for Jameson to inject a plug about SODA
every now and then.

My main reservation about SODA at this point is that I see no practical
path to adoption.  It would be perfect for a large primary, like the
current Republican presidential field, but there's no way to start at that
level.  We have to start small.  But for small political elections,
professional societies, open source decisions, elementary school elections
etc. it seems too complicated.  I had a long discussion with a party
district chairman here.  He's interested in alternative voting systems to
fill his party positions but skeptical of complexity.  I don't even think
I've pitched him on SODA because he's still thinking about Approval Voting.

And with SODA, you can't just run a straw poll to show it off like you can
with so many other voting systems.  You need the participation of the
actual candidates to choose their rankings beforehand and to do their
delegation afterwards.

I know we haven't traditionally discussed implementation strategy on this
list (though that has changed some recently), but if you see a good
strategy for SODA adoption, please tell.

~ Andy



On Tue, Dec 13, 2011 at 6:55 PM, Jameson Quinn <jameson.quinn at gmail.com>wrote:

> I believe that LRV (Least Resentment Voting) is indeed quite a clever
> solution to the chicken dilemma. But once more, I'd like to remind people
> that there is a way to solve the chicken dilemma without risking a victory
> by the plurality winner/condorcet loser. I'm speaking of course of SODA.
>
> First, SODA meets the FBC. In fact, in any 3-candidate scenario, and I
> believe in any 4-candidate one, it is strategically optimal to bullet vote
> for a candidate if you agree with their declared preferences. This ability,
> not just to vote your favorite equal-top, but unique-top, is not shared by
> any other method I know of. (Perhaps we could call this UFBC3, unique FBC
> for 3 candidates.)
>
> How does it do with chicken dilemma scenarios? For the following, I'll
> give honest ratings, then discuss the likely strategic implications under
> SODA.
>
> 40 C
> 25 A>B
> 35 B>A
>
> If this is the honest situation, then candidates A and B have every reason
> to find a way to include each other in their predeclared preference lists.
> These predeclared lists are made openly, and so one side cannot betray the
> other without giving the other side a chance to retaliate. The chance for
> retaliation will make betrayal a losing strategy.
>
> 40 C
> 25 A
> 35 B>A
>
> If the A camp is honestly indifferent between B and C, and candidate B
> finds this indifference credible, then B can still decide not to retaliate,
> that is, to ignore A's truncation and nonetheless declare a preference for
> A. This enables A to win without B spoiling the election.
>
> (Any single-round method which elects A here is subject to the chicken
> dilemma; electing B is, in my mind, crazy; and any method which elects C
> here has been spoiled by candidate B, and so encourages shenanigans of the
> republicans-funding-greens sort. Any method I know of except SODA fails in
> one of these ways.)
>
> 40 C
> 25 A>B
> 35 B
>
> This is like the above situation, but since A had no chance of winning
> anyway, they have even less of a motivation to retaliate against B, whether
> or not B's truncation is honest.
>
> 40 C>>A
> 25 A>>B
> 35 B>>A
>
> In this situation, it's difficult to say who's the "correct" winner;
> depending on the underlying utilities, it could easily be any of the three,
> so I'd have no problem with a method that elected any. Still, ideally a
> method would give similar results here as in the situations above, so that
> candidates and voters are not motivated to be conciliatory, rather than
> projecting an image of someone who's inclined to truncate.
>
> Strategically, it is in B's interest to truncate, to reduce the chance of
> 10 C>>A voters voting CA and thus giving A the all-important second move in
> the vote delegation stage. Then, candidate A will declare a preference for
> B, in order to present C with a credible threat. And candidate C will
> declare a preference for A to prevent B from winning.
>
> 40 C>>A???
> 25 A>B
> 35 B>>A???
>
> This is the "weak condorcet winner" situation. The question marks denote a
> "preference" for the dark-horse candidate A which would evaporate in a
> runoff, when people took a hard look at A without being distracted by the
> C/B rivalry. If that is the case, A should not win. And indeed, even if C
> predeclares a preference for A, when C is faced with the morning-after
> reality of the choice to throw the election to A or allow it to go to B,
> they have a chance to leave it with B if A is really such a bad candidate.
> Sure, C may prefer a weak winner who owes them a favor to a stronger
> opponent, and so elect A even if B would be socially-optimal; but at least
> SODA gives B a chance in this situation. Any Condorcet method would simply
> elect A and not look back.
>
> I think that the situations above show that SODA always allows honest
> truncation without a strategic penalty, but does not encourage strategic
> truncation.
>
> I know that some people on this list dislike SODA for its delegation.
> Obviously, I disagree. Consider:
> - SODA delegation is optional and eyes-open. Because of pre-declaration,
> you know what kinds of result your delegated vote could and could not
> promote, and if you don't like those results, you don't delegate.
> - SODA delegation allows results that seem to me to be obviously better
> than other methods in the above scenarios.
> - SODA delegation allows for unmatched simplicity from the average voter's
> perspective. If you like your favorite's declared preferences, just vote
> for them, and you're done.
> - SODA delegation allows significant minority candidates a moment of
> personal power, which they can use to extract (non-binding) promises before
> throwing their votes behind someone. I believe that this transitory moment
> of minority power is a healthy compromise between the stability and
> leadership in winner-take-all systems and the broader accommodation of
> minority interests in parliamentary systems.
>
> Of course, there are cases where SODA is not ideal. For instance, for a
> pre-election poll, SODA cannot be used unless the inter-candidate
> preferences can be somehow known or inferred. Still, I think SODA is
> overall a standout good method for most cases where high-stakes
> single-winner elections are appropriate.
>
> Jameson
>
>
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