[EM] possible improved IRV method

[Rob LeGrand]

Allen wrote:
> Yes, it looks like you proposed the same thing back in 2002.
> What became of your proposal? ;-)

Some members of the instantrunoff-freewheeling group were arguing for the
superiority of IRV over Condorcet.  Double IRV was one of my attempts to
seduce them to the Condorcet side.  Success was quite limited.  BTR-IRV
was a bit more successful, but I have since decided that there's little
to gain from promoting an IRV-like Condorcet method.  I think many real-
world voters would order-reverse under Cordorcet just like they would
under Borda (though many others would vote sincerely under any method).
These days I see Approval and Range Voting as much better reforms.

> Getting back to Condorcet, there is a majority in each pair-wise
> comparison, but for each pair, it is a different set of voters.  There
> is no way, at the end of the election, to go back and say "This is the
> majority that elected the winner".

Sure there is, and it's no more arbitrary than IRV's way.  Simply take
the slimmest majority victory.  Of course, this looks pretty empty if
there is no voted Condorcet winner and the winner of whatever Condorcet
method you're using does lose some pairwise race.  But pointing out that
winner's slimmest *victory* still is no more arbitrary than the one IRV
finds in the last round.  (Of course, this only works if the Condorcet
method never elects a Condorcet loser; the best ones never do.)

> Note I believe I may have been incorrect about my previous proposal
> meeting the Condorcet criteria.  While under that proposal a candidate
> can only be eliminated if he loses a pair-wise comparison, the
> comparisons happen after candidates have been eliminated and votes
> redistributed.  This would seem to have some sort of effect, but I'm
> still hashing it over.

No, your proposal is indeed Condorcet-compliant.  The last comparison to
decide on each eliminated candidate is pairwise, so every eliminated
candidate must lose at least one pairwise comparison.  Therefore a voted
Condorcet winner can never be eliminated and will win.

> In addition, the ideal voting system to be monotonic.  Classic IRV is
> recognized as not monotonic.  One of the goals of my proposal was to at
> least find a monotonic method.  I don't know if it accomplishes this of
> not.

I think you will find it very difficult to create a monotonic method that
uses elimination rounds--unless you do something silly like repeatedly
eliminating the candidate with the lowest Borda score without
recalculating scores (which would simply elect the Borda winner).

> With respect to "strategic voting", I believe the ideal voting system
> would be essentially immune from strategic voting.  Each voter would
> state their sincere preferences, and the tabulation would be
> responsible for determining the winner as if each voter had executed
> their optimal strategy.

There has been some research into this issue both on this list and in
academia.  Check out Lorrie Cranor's dissertation work on Declared-
Strategy Voting at http://lorrie.cranor.org/dsv.html .  My current
doctoral work is related to hers.

--
Rob LeGrand, psephologist
rob at approvalvoting.org
Citizens for Approval Voting
http://www.approvalvoting.org/

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