[EM] A method "DNA" generator, tester, and fixer

[Juho]

On May 27, 2010, at 3:01 AM, Kevin Venzke wrote:

> Hi Juho,
>
> --- En date de : Mer 26.5.10, Juho <juho4880 at yahoo.co.uk> a écrit :
>>>> The following criterion is similar to
>> Plurality.  Does
>>>> it have a name?
>>>>
>>>> If the number of ballots on which X beats Y is
>> greater than
>>>> the number of
>>>> ballots on which Y is ranked, then Y cannot be
>> elected.
>>
>>>> Any decent method that doesn't satisfy it?
>>>
>>> This criterion is strictly stronger than Plurality, so
>> I'd have to ask
>>> whether you think any decent methods fail Plurality.
>> Probably the answer
>>> is no, not really.
>>
>> This says that all typical margins based Condorcet methods
>> would not be "decent". One could ask the question also in
>> the reverse direction. All methods violate some criteria
>> that look good at least at first sight. Which property of
>> the plurality criterion (or the new criterion) makes it a
>> mandatory requirement for all election methods (or Condorcet
>> or ranked methods)?
>
> Personally I would allow Plurality failures for a good reason.
>
> But I think that most people would generally not be accepting. This  
> would
> be because of a view that there is such a thing as "support"  
> involved in
> voting for a candidate and this can't be found when one truncates a
> candidate. So when you compare a candidate X who is the favorite of 10
> voters, and you can't find that many voters who "support" Y on their
> ballots in any way, something seems wrong when Y wins. The thought is
> why would you ever need to elect Y when you could just elect X? It's
> similar to Pareto in that sense.

Yes, in ballots where the position of truncated (or shared last)  
candidates looks clearly different than the position of other  
candidates the voters may get the impression that thy are supporting  
all others and not supporting the truncated / shared last candidates.  
And they may vote this way and dislike methods that do do not respect  
their impression on what should happen with respect to candidates with  
lots of first preferences vs. candidates with less any higher than  
last preferences. But on the other hand all methods need not have such  
implicit approval/support assumptions.

It depends also a lot on the environment if one should optimize the  
method so that it will perform well under all (sincere and/or  
strategic) circumstances or if it should look good to the average  
voters and politicians so that it will have a chance of getting  
adopted. If one wants e.g. to promote Condorcet methods one could (in  
theory) listen to the discussion for a while and then pick a method  
that looks best in the observed discussion environment (the behaviour  
of all Condoret methods is anyway quite similar in typical elections).

There could be also other criteria that people want to see  
implemented. They might for example hate "favourite betrayal", and  
that could make all Condorcet methods unusable. If people study  
election methods in detail they must accept that all the best election  
methods will violate some nice looking criteria.

Btw, in the example above I guess the plurality criterion doesn't  
requite that X should win. Also some other candidate with sufficient  
number of above last rankings could win. In that sense methods that  
meet the plurality criterion might not be an exact match to the needs  
of that voter who wanted X to win with 10 votes.

>
> Really I have no idea what Forest has in mind by "decent." Maybe he
> does find margins or MMPO to be decent. I believe he even accepts  
> random
> methods if there's a point to them, so who knows.

Random methods are an interesting group here. I tend to see  
deterministic ((except when we have exact ties)) methods as methods  
that should be used by default in most elections. But there can be  
also methods where random/probabilistic choices are acceptable or  
maybe exactly what we want. In the same way I tend to see the  
compromise seeking nature of Condorcet methods to be appropriate for  
most single-winner elections, but also in this case, there could be  
elections where we have some other targets. Also elections where the  
ballots should collect approvals / list of supported candidates and  
the method should put lots of weight on these measured opinions are  
possible. I'm just not sure if that should be the main rule or  
reserved only for elections where such properties are really needed.

Juho


>
> Kevin
>
>
>
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