[EM] MAV on electowiki

Chris Benham cbenhamau at yahoo.com.au
Thu Jun 27 09:35:04 PDT 2013


"I don't see it..."

Say on an ABCD grading ballot you give your Lesser Evil X a B, and then in the second round both X and  your Greater Evil Y reach the majority threshold. In that case you obviously might have cause to regret that you didn't give X an A.

That is why your suggestion makes it (even) less safe to not simply give all the acceptable candidates an A.

"I think that's [IBIFA] a great method, but I would classify it as "improved Condorcet" rather than "Bucklin-like".

No. There isn't any pairwise component in the algorithm, and unlike the "Improved Condorcet" methods it doesn't directly aim to come as close as possible to meeting Condorcet without violating Favorite Betrayal.

But another method I support is in that category, "TTPBA//TR".  Mike Ossipoff  promoted it as "Improved Condorcet, Top"  (or ICT).


Chris Benham

Jameson Quinn wrote (27 June 2013):

2013/6/26 Chris Benham <cbenhamau at yahoo.com.au>
> Jameson,
> I don't like this version at all. These methods all have the problem that the voters have a strong incentive to just submit approval ballots, i.e. only use the top and bottom grades.

You are right... if they believe that all other voters will act the same way. But if experience has shown that there are enough "honest" voters so that winning medians¹ tend to be in a given range, then it is safe to vote expressively outside that range. 

¹ Actually, as long as your vote for your preferred frontrunner is above the second-place median, and your vote for your less-preferred frontrunner is below the first-place median, your vote is strategically optimal.
> Your suggested way of determining a winner among candidates who first get a majority in the same round only makes that incentive a bit stronger still.

I don't see it. The MAV completion method is as close to later-no-harm as is possible in a Bucklin system; which tends to balance out the later-no-help. I think you're the one who's pointed out before that passing one and failing the other is usually worse than failing both; by the same token, if one is passed by all Bucklin systems, then the Bucklin system which fails the other by the least is the best. 

> I agree with a Mike Ossipoff suggestion, that we elect the member of that set of candidates with the most above-bottom votes.

That completion is fine. My larger point is that it's silly to fight about these issues. We should settle on one Bucklin proposal and stick to it. I currently believe that MAV is most viable in that sense, but I'd be happy if you got enough support for the Ossipoff suggestion to convince me otherwise. 

> Also, given the strong truncation incentive, I think 5 grades is one too many. In my opinion 4 grades would be adequately expressive.

I personally slightly prefer 5 grades. It increases the probability that a voter who wants to be strategic and confidently knows the expected range of possible winning (and second-place) medians, will have room to make purely-expressive distinctions at the top and/or bottom of the ballot. In other words, if you know that the winner always gets a C, then it is strategically safe to make honest distinctions between A/B or between D/F. 

But that's a slight preference. If demonstrate that your position has more support among the active posters here, I'd join with you for the sake of unity.

> My favourite Bucklin-like method is "Irrelevant-Ballot Independent Fallback-Approval" (aka IBFA) that I introduced in May 2010.
> http://lists.electorama.com/pipermail/election-methods-electorama.com/2010-May/026479.html 

I think that's a great method, but I would classify it as "improved Condorcet" rather than "Bucklin-like". I think it would be productive to do the same work for the improved Condorcet systems that I'm trying to do with Bucklin: that is, to settle on a single simple proposal that people can agree is among the better options (even if they can't agree it's best), and find a simple descriptive name for that proposal. I expect IBIFA would be a strong contender in that process. It's possible that in the future, Bucklin and Improved Condorcet advocates could agree to join forces, but I suspect it's premature for that at the moment. 

If you disagree with the above, I'd be interested to hear how you see it.

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