[EM] IRV is best method meeting 'later no harm'?

[Raph Frank]

On Thu, Nov 26, 2009 at 8:52 PM,  <seppley at alumni.caltech.edu> wrote:
> Similar to truly condorcetian methods, Withdrawal//IRV would presumably
> tend to elect candidates who take median positions on the issues.  That
> would create an incentive for candidates who want to win to take median
> positions.

That assumes that candidates would put the interests of their
constituents first.  They are more likely to play chicken and hope one
of the other candidates stands down.

One possible option would be to allow withdrawal once they have just
been eliminated.

For example, the you could have a rule that the 2nd place candidate in
gets to withdraw after the election.  In effect, you run IRV once and
then run it again with the 2nd place candidate withdrawn.  The 2nd
place candidate in the first pass gets to pick which of the 2 winners
wins (if different).

> I'm not claiming median positions are necessarily best.  But I do believe
> there are significant advantages to voting methods that induce candidates
> who want to win to take median positions:  Less polarization and less
> demagoguery.

Right.  Also, one of the advantages of PR, is that legislature control
doesn't snap from one party to the other after an election.

A plurality election system might give stability for the duration of
the term, due to large majorities, but

> By the way, if my understanding is correct, IRV is not Single Transferable
> Vote (STV), the single-winner voting method used in Australia & Ireland.
> IRV severely limits the number of candidates each voter can rank (to 3, if
> my understanding is correct) whereas STV allows (or requires) each voter
> to rank every candidate.  STV satisfies LNH, and many people may consider
> it to be somewhat better than IRV. (STV facilitates greater competition
> and less spoiling, especially if candidates are permitted to withdraw
> after the votes are cast.)

No, IRV is the single seat method with unlimited votes.  However,
Fairvote seem to have used the term for lots of different methods,
even when not strictly correct.

> Since IRV is said to satisfy LNH, then one must say Plurality Rule
> satisfies LNH too, because Plurality Rule can be viewed as just a
> variation of IRV with a smaller limit (one candidate per voter).

The definition doesn't really apply to plurality.  It says that giving
a ranking to candidate can never hurt candidates which you have ranked
higher.

This is true in IRV as they don't even look at your lower ranks until
that candidate has been eliminated.