[EM] Unranked ballot election challenge

[MIKE OSSIPOFF]

Tom wrote:

>*** FBC= "Favorite Betrayal Criterion - By voting another candidate over 
>his
>favorite, a voter should never get a result that he considers preferable to
>every result he could get without doing so."
>
>I'm not sure what "voting over one's favorite" means with unranked ballots.

Let me ask you: If you can give any candidate one vote or zero votes,
then how could you vote A over B? If you vote for A and you don't
vote for B, are you voting A over, under, or equal to B?

Actually, for criteria, I have a general definition that I use,
and which I've posted here during the time that you have been on EM:

A voter votes A over B if he votes in a way so that it's possible to
contrive a configuration of the other people's votes such that if
we delete from the ballots everyone except A & B, then A will be the
unique winner if & only if we count that voter's ballot.

Likewise I've posted a definition of sincere voting.

>Surely leaving a favorite unranked CAN NOT help one's favorite.

No, but FBC doesn't say anything about leaving one's favorite unranked.
Voting someone over your favorite can benefit you with most methods.
Approval & CR are the only methods known to never give you any strategic
need to vote someone else over your favorite. I still don't know
if Condorcet passes FBC.

Offering a
>tie with another to help defeat a least liked choice seems an identical
>compromise under Unranked IRV as Approval.

But the question is, will it always work in UIRV, or will you sometimes
have to vote that compromise and not for your favorite? As I said,
I'll check for a badexample, and will post it when I find it.

>Approval and Unranked IRV both demand polling information to allow voters 
>to
>consider how far to compromise. I see both methods as suffering from
>spoilers in the sense that voters are encouraged to vote ALSO for a 
>stronger
>second favorite. However I see no spoilers in the sense of voter being
>encouraged to NOT voting for one's favorite at all.

If you vote for your favorite, you give less to your compromise, and
might in that way let your compromise get eliminated, electing your
last choice. As I said, I'll post an example within a few days,
unless (unlikely) one can't be found. It's a simple enough method that
it shouldn't be so difficult to find an FBC failure example.

>
>Under what conditions in Unranked IRV would a voter benefit from bullet
>voting for a second favorite? I'm sorry, but I can't see this.

Say your 2nd choice needs your help to not be eliminated, to keep
your last choice from winning. Say that dividing your vote between
Favorite & Middle won't give Middle enough to save him from immediate
elimination.

That's just a verbal scenario outline. An example will be along within
a few days unless (unlikely) there's no easily-found badexample.

Obviously, until I send an example, I can't say for sure that UIRV
fails FBC.

Mike Ossipoff


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