[EM] PAR is awesome part 1/2: FBC?

[Jameson Quinn]

2016-11-12 10:45 GMT-05:00 C.Benham <cbenham at adam.com.au>:

> On 11/12/2016 7:53 AM, Jameson Quinn wrote:
>
>
>
> 2016-11-11 12:50 GMT-05:00 C.Benham <cbenham at adam.com.au>:
>
>> On 11/11/2016 10:14 PM, Jameson Quinn wrote:
>>
>> I think that simple PAR is close enough to FBC compliance to be an
>> acceptable proposal.
>>
>>
>> I'm afraid I can't see any value in "close enough" to FBC compliance.
>> The point of FBC is to give an absolute guarantee to (possibly uninformed
>> and not strategically savvy)  greater-evil fearing voters.
>>
>
> Yes. The guarantee you can give is "as long as the world is somewhere in
> this restricted domain — that is, essentially, as long as there are no
> Condorcet cycles and each voter naturally rejects at least one of the 3
> frontrunners — this method meets FBC". This is much broader than any
> guarantee you could give for a typical non-FBC method. For instance, with
> IRV, the best you could say would be "as long as your favorite is
> eliminated early or wins overall, you don't have to betray them", which
> unlike PAR's guarantee is not something which could ever be generally true
> about all real elections for all factions.
>
> C: I have in mind voters who are inclined to Compromise, and so it's *
> absolute guarantee* or it's nothing.   Smith//Approval also has a much
> lower Compromise incentive
> than does IRV  (which in turn has a much much lower Compromise incentive
> then FPP).
>
>
>
>
>>
>> It elects the "correct" winner in a chicken dilemma scenario,
>> naive/honest/strategyless ballots, without a "slippery slope" (though of
>> course, this is no longer a strong Nash equilibrium).
>>
>>
>> How do you have a "chicken dilemma scenario" with
>> "naive/honest/strategyless ballots" ?
>>
>> 35: C >> A=B
>> 33: A>B >> C
>> 32: B >> A=C  (sincere is B>A >> C)
>>
>> In this CD scenario your method elects B  in violation of the CD
>> criterion.
>>
>
> You're suggesting that the sincere preferences are
>
> 35: C >> A=B
> 33: A>B >> C
> 32: B>A >> C
>
>
> C:  I'm not "suggesting". I'm stating.
>
>
> If you are 1 of the B>A>>C voters considering whether to strategically
> vote B>>A=C, you have no strong motivation to do so, because your vote
> alone is not enough to shift the winner to B. This is what I mean by "no
> slippery slope".
>
>
> C: One "vote alone" is very rarely enough to do anything, so I suppose
> no-one has a "strong motivation" to vote.
>

In Smith//approval, one vote alone would shift the above honest election;
so the fact that it does not in PAR is indeed notable.

In particular: in PAR, there is no way for the B voters to strategize such
that they win the above election, while still ensuring that C does not win
no matter what the A voters do. This "safe" strategizing is grease on the
slippery slope.


>
>
> I believe that in the election you gave, there is no way to tell what the
> sincere preferences are.
>
>
>
> C: From just the information on the ballots, of course not (like any
> election).
>
>
> Perhaps the B voters are strategically truncating A; perhaps the C voters
> are strategically truncating B. So the "correct winner" could be either A
> or B, but is almost certainly not C.
>
>
> C: By "correct winner" I assume you mean the sincere CW. But there is
> reason to assume there is one. And if the B voters are actively Burying C,
> it could be C.
>
> The "CD criterion" requires the system to elect C, merely to punish the B
> voters; I think that's perverse, because, among other things, it means that
> a system does badly with center squeeze, allowing the C faction to
> strategize and win.
>
> C: No, it merely says "not B".  But CD + Plurality say that it must be C.
>
>
>
>>
>> Since you are apparently now content to do without FBC  compliance  and
>> you imply that electing the CW is a good thing,
>> why don't you advocate a method that meets the Condorcet criterion?
>>
>> What is wrong with Smith//Approval?  Or Forest's nearly equivalent Max
>> Covered Approval?
>>
>
> Largely, it's because I think that Condorcet systems are strategically
> counterintuitive, and hard to present results in. I think that will lead to
> more strategy than a system like PAR. That's because PAR can make
> guarantees that Condorcet systems can't.
>
> C: Such as?  What exactly does "strategically counter-intuitive" mean?  An
> example?
>

What I mean is that if you take a non-election-theorist, present an
election scenario to them, explain who won and why, and ask how they would
strategize in the place of voter X, they are more likely to suggest
counterproductive strategies, and less likely to see any strategies that
actually might work, in Condorcet than in Bucklin-like systems.


>
> In a system like MJ or Score, you can give a number to each candidate,
> based on their own ratings alone, and the higher number wins. That is an
> easy way to get monotonicity, FBC, and IIA.
>
> In Condorcet, no candidate has any number except in relation to all other
> candidates. That's good for passing the Condorcet criterion (obviously) but
> it breaks FBC and IIA.
>
> C:  Your method and MJ fail IIA.
>

MJ passes IIA. PAR fails it, as you say, but passes LIIA.
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