[EM] Comments on some rank methods

Kristofer Munsterhjelm km_elmet at lavabit.com
Tue Apr 10 12:27:14 PDT 2012

On 04/09/2012 11:31 PM, MIKE OSSIPOFF wrote:
> I've said seemingly contradictory things about IRV. It's particularly
> flagrant FBC failure makes it entirely inadequate for
> public political elections, more so than Condorcet, which, too, is
> inadequate due to FBC failure.

You keep saying anything without FBC is automatically a no-go. How do 
you know that? Condorcet elections seem to work well where they're used: 
in the Pirate Parties, in Debian, on Wikimedia, and in smaller 
organizations (see the Wikipedia article on the Schulze method for more).

IRV's compromise problem is particularly bad. In a Burlington scenario, 
the voters (and/or parties) immediately know they didn't compromise well 
enough. In contrast, that doesn't happen in Condorcet, because it picks 
the CW.

I suppose you could argue I'm making the same mistake as the IRVists. 
The IRVists say "oh, we need a way of not making small third parties get 
in the way of the major parties - here's a fix". You might argue I'm 
saying "oh, we need a way of the method not messing up when third 
parties get reasonably large - here's a fix, in the form of Condorcet 
compliance". But if I'm just proposing a fix and the fix isn't 
substantial, then we should be seeing backsliding from Condorcet where 
it's used, and I don't know of any such.

> And I also said that IRV would be a fine method, were it not for the
> public's inclination towards resigned, cowed overcompromise,
> and their very sad and disastrous lowering of standards for
> acceptability. "Vote for the least bad of the corrupt candidates,
> because they're the
> winnable ones".

I disagree. Look at Burlington with its center squeeze again. The 
Burlington voters didn't strategize (much or effectively). Yet instead 
of picking the candidate closest to the median voter, IRV threw that one 
away because it didn't have enough first-place votes and picked the 
largest wing instead.

Sure, it's better than Plurality. It's not as polarizing as Plurality, 
either, but it does have some element of polarization in picking the 
largest wing.

> But how could IRV be alright, even with better voting? Wouldn't people
> wanting to maximize their expectation still favorite-bury sometimes?
> Sure. But if their judgement was at all reasonable, they wouldn't do so
> in a way that would bother me. It comes down to what one calls
> "acceptable".
> IRV's strategy in non-u/a elections would be especially complicated to
> describe, but it's a sure thing that it would often involve favorite-burial,
> to maximize a voter's expectation. Without knowing the details on how to
> vote (no method matches Approval's clearly-defined simple strategy,
> for any kind of election), voters would still do favorite-burial.
> As with Approval, and probably all methods, IRV's expectation-maximizing
> strategy is simpler in a u/a election. But that doesn't mean that
> it's simple enough for anyone to know what it is, exactly.

How about this zero-info: Rank all the acceptables in alphabetical 
order. Rank the unacceptables in random order after the acceptables. By 
ranking the acceptables in the same order, you focus the first 
preference votes on a few candidates so that compromise is maximized; by 
ranking the unacceptables randomly, you discourage strategy that 
attempts to compromise with your pattern (because there is no pattern).

If you have information, then rank the acceptables in order of first 
preference votes, then the unacceptables in reverse order of first 
preference votes. There might be better strategies that would make use 
of later-round data, but I think that data would be hard to come by.

If you can poll ranking data, you could in any case just do so and then 
use a computer to find your optimal ballot (or the optimal ballot for 
your coalition). For IRV, the strategy algorithm is worst-case 
exponential time with respect to the number of candidates, but in 
practice that doesn't matter. When there are loads of candidates, some 
will have no chance and so not contribute to making strategy harder.

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