[EM] FairVote comment on Burlington dumping IRV

[Jameson Quinn]

OK. I think we can work this out. Before I make more arguments, I'm going
to try to explain the disagreements as I see them, and ask you more about
what you're saying.

A. MAV vs. ER-Bucklin (ERB, though we should probably find a better name at
some point). That is, completion using above-median, or completion using
median-or-above.

I don't see a huge difference here. I think MAV is slightly better because
of the chicken dilemma, but it's possible that that regular voters would
see ERB as simpler by a big enough margin to make it worth supporting
instead. I'm probably not a good judge of that because my mathy brain tends
to see them as exactly symmetrical.

I think you're beginning to understand my point about symmetry. Your view
is that ERB is better because of apparent simplicity (empirical question
about voters; we could find agreement here with more evidence) and also
because of some Deep Principle of counting all the votes which I don't
understand (because in my view MAV and ERB are *exactly* as likely to
"count a given vote" or not, that is, to make a given gap in ratings
between two candidates significant or not). I'm not sure that explaining
your Principle further would help me understand it, because it's probably
not going to fit with my logic. I would, however, like to understand more
about whether you see the simplicity or the Principle as more important
here.

B. MAV vs. EMAV

On this question, our principal disagreement is around the strategic impact
of the voting system, both for general exaggeration and for specific
chicken dilemma scenarios. Here's my logic:

...Start Jameson's logic...

1. In different systems, different strategies are effective. I'll give one
"5 candidate linear" (5CL) scenario and one chicken dilemma (CD) scenario
to illustrate my point.

Honest utilities
5CL:
23: L100, CL75, CR25, R00, RR00
25: L50, CL100, CR50, R00, RR00
24: L00, CL50, CR100, R50, RR25
22: L00, CL25, CR75, R100, RR50
06: L00, CL00, CR25, R50, RR100

(To make this comparison clearer, I'm going to use 4+1 ratings for both
systems, though it would actually work the same if under EMAV, "25"
represented a coinflip between the closest available ratings, 50 and 0)

CL is the honest winner under both MAV and EMAV, with a median of 50. Under
both systems, the CR voters could win by dropping CL's rating to 25, and
the CL voters could defend against this by dropping CR to 25. Under both,
the RR voters could elect CR by rating them at 75 or above. But EMAV
presents a number of further possible strategies: for instance, the R and L
voters could both help their preferred frontrunner by rating CR and CL at
100 and 0 or vice versa, whereas with MAV these strategies would have no
impact.

CD:
40: L100, RA0, RB0
31: L0, RA100, RB75
29: L0, RA75, RB100

RA is the honest winner under both systems. Under both, RB could win if his
voters drop RA's rating to 25 (a risk-free strategy), and RA voters could
defend by dropping RB to 25. Under both, RB voters could still win by
taking the risky step of dropping RA to 0, but if RA voters "defensively"
or "in retaliation" took a similar step, then L would win.

But in EMAV, only 7 RB voters would have to drop RA from 25 to 0 in order
to win, while in MAV it would take at least 20 of them. Since the 7 it
would take in EMAV do not in themselves create a risk of L winning, it
would behoove 13 RA voters to defensively downrate RB so that it would take
a risky 20 extreme-strategy RB voters to win. But this slippery slope
continues, and pretty easily, through miscoordination or over-risky
strategies, L could end up winning. In MAV, such problems are less likely,
as any extreme strategy that might win is also inherently risky; instead of
a long and slippery slope, MAV gives a flat buffer and then a sharper cliff.

2. I believe that candidates, pundits, and/or voters would realize the
different strategic potential of MAV versus EMAV, leading to significantly
more-exaggerated votes under EMAV.

3. I believe that the BR downside of that additional strategy would be
greater than the BR upside of EMAV's greater sensitivity to honest votes.

....End Jameson's logic...

>From what I understand, you (Abd) disagree with point 2 above on both
empirical and philosophical grounds. That is, you think empirically that
people will not in practice exaggerate more in EMAV vs MAV; and
philosophically, that if people did exaggerate, that doing so would be a
moral choice which shed light on their truer underlying utilities, so that
whatever result EMAV gave in that case would actually not be a worse BR.

I can, to a certain extent, understand both of these points. I think that
the philosophical point is, to a certain degree, moving the goalposts; if
your model doesn't allow honest and voted utilities to differ, then of
course Score-like systems will come out better. But from another
perspective, it's just the converse of your empirical point; that is, if
your empirical point is "people won't exaggerate", then your philosophical
one is just adding "unless they actually mean it".

Am I characterizing your arguments fairly? If so, how do they apply to the
two specific scenarios above?

I'll stop here, and won't argue further until I'm confident we understand
each other.

Jameson
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