Approval and twins

[Blake Cretney]

On Wed, 28 Oct 1998 18:02:56   Mike Ositoff wrote:
>> 
>> I consider rich-party and vote-splitting to be two of the most
>> important problems, so I think it's important to ask how well
>> approval does in regard to them.
>> 
>> Certainly, approval passes GITC.  However, GITC was designed
>> for rank methods.  In theory, plurality passes GITC.
>
>In no way could Plurality be said to pass the Clone-Independence
>Criterion, if that's what GITC refers to. If an added clone
>splits the vote, it could make the former wininer in the clone
>set lose.

Technically, any candidate who receives a vote in plurality is 
not a clone, since it has been differentiated from all the other 
candidates.  Of course, this doesn't mean that vote-splitting 
doesn't work, just that we should be careful using GITC to test 
non-ranked methods for these problems.  In fact, as I've
mentioned before, we should be careful about methods that
don't allow equal rankings too.

>
>You say that Approval passes GITC. If GITC is designed for rank
>methods, but Approval passes it anyway, I guess I don't understand
>what the problem is.

The problem is that the fact Approval passes GITC doesn't prove
it doesn't have the rich party and vote-splitting problems.

>> In ranked methods, a voter can differentiate between the
>> members of a party, and still rank those members higher than
>> anybody else.  This is not possible with approval.  In
>> approval, a voter must decide whether to help the party as
>> much as possible, or to differentiate between members of
>> the party.  And if voters tend to vote purely along party
>> lines, the choice within the party could be made by very
>> few people.

>Meaningless. A rational voter doesn't base his vote on
>party loyalty. Not everyone is so party-oriented.

Few voters would base their vote on a blind allegiance to a party
name.  However, if the members of a party have similar policies,
it is very likely that a voter may prefer any of them to any
other candidate, but still have preferences within the party.

Of course, this is the assumption on which the idea of clones is
based.

>
>> 
>> There are two strategies that I can imagine voters employing.
>> They will largely be psychologically determined, so it would
>> be necessary to find out which is used by polling and
>> observation.
>> 
>> Except Worst
>> The voter votes for most members of the party, but withholds from
>> a few of his least favorites.
>> 
>> Only Best
>> The voter votes only for a few of his favorite candidates from
>> within his party.
>> 
>> If a party thinks its voters fall into the "Except Worst" category,
>> then it makes sense to run more candidates, and thereby spread out
>> the "No" votes.  If on the other hand they follow the "Only Best"
>> strategy, it makes sense to run fewer candidates in order to
>> concentrate the "YES" votes.

>Approval has more than 2 strategies, that I've read of. The ones
>you list aren't among the ones I"ve read of or would use.

I suspect I would end up voting like the "Except Worst".  How would
you balance the desire to get a party whose policies you support
elected, with the desire to choose from within that party?

>> If a party thinks its voters fall into the "Except Worst" category,
>> then it makes sense to run more candidates, and thereby spread out
>> the "No" votes.  If on the other hand they follow the "Only Best"
>> strategy, it makes sense to run fewer candidates in order to
>> concentrate the "YES" votes.

>Approval gives no incentive to "concentrate" votes. A party
>runs the best candidates it can, and lets anyone run who wants
>to, since people can vote for him without abandoning other's.

As I say, it depends on how people vote.  If people are too picky,
then running more candidate will hurt a party, since the factions
of a party will only vote for their own candidate and the vote will
be split.

---
Blake



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