[EM] Fwd: Fwd: U/P voting: new name for simple 3-level method.

[Jameson Quinn]

2016-09-10 21:26 GMT-04:00 C.Benham <cbenham at adam.com.au>:

> On 9/11/2016 5:02 AM, Kevin Venzke wrote:
>
> 43: A
>> 24: B>C
>> 23: C>B
>> 10: D
>>
>> Under MTA the B and C voters are being completely reasonable: They hope
>> for majority approval but can still hope for a win if they
>> don't get it.
>>
>> Strategy is less likely to produce these ballots under U/P because the B
>> and C voters are taking a gamble. To get a similar outcome
>> they have to vote B=C. Anyone who doesn't is functionally defecting!
>>
>
>  C: A very good example!   Assuming MTA and MCA use Top Ratings scores to
> break Approval ties, they both elect the Condorcet winner B.
>

But both could be shifted to C with a single C-only ballot, even if the B:C
ratio were 46:1 instead of 24:23.


>
> U/P's under-use of  the middle ratings slot means that it relies more on
> its "majority disqualification" mechanism which seems to make it more
> vulnerable to irrelevant ballots, as in the example.
>
> Under U/P, without the irrelevant D ballots, A and D are disqualified and
> B is the glorious winner. With them, B and C and D are disqualified and
> (without needing
> any others to be disqualified) A wins.
>
> This causes me to reject U/P as clearly worse than MTA and MCA. Of the
> three I (again) rate MTA as the least bad.
>

I think MTA is pretty darn good. I still prefer U/P.

I think that scenarios like the above are fundamentally pathological; any
possible winner has only minority approval, so that even assuming all
ballots are semi-honest, any of them could be a true Condorcet loser. Thus,
I believe that it's more important for a system to try to avoid scenarios
like the above, than to try to find a perfect winner in such a scenario. In
fact, in the related scenario:


43: A
40: B>C
6: C>B
1: C
10: D

... I think that a case can be made for either A or B. After all, they'd be
tied if we try to approximate Score by using truncatable Borda here. But no
serious case can be made for C or D, even though C wins MTA and MCA.

Anyway, I think U/P does a better job trying to discourage the kind of
strategy that would lead to a scenario like the above. And part of that is
the default rule which Chris has criticized.

One possible alternative default rule: ballots alternate between defaulting
to "acceptable" and to "unacceptable". Each ballot clearly states which
default it uses, and there is a place on the ballot to globally change that
default. (I doubt Chris will like this idea, but it is at least
straightforward, explicit, and easy to describe.)


> Chris Benham
>
>
>
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