[EM] Why I Prefer IRV to Condorcet

[Chris Benham]

Kristopher,
All Condorcet methods are vulnerable to Burial. Smith,IRV has in 
common with IRV but not the other well-known Condorcet methods
that a Mutual Dominant Third winner can't be buried. But like all other
Condorcet methods it is not absolutely invulnerable to Burial like IRV.

37: A>B
31: B>A
32: C>B

B is the CW, but if the A>B voters bury B by changing to A>C then
the Smith,IRV winner changes from B to A.

For the advantage over IRV of the difference between Smith and
Mutual Dominant Third (MDT), we lose Burial Invulnerability and
Later-no-Harm and Later-no-Help and Mono-add-Top.

So I think the argument that Smith,IRV is really much better than the
simpler plain IRV is weak. Likewise the case that Smith,IRV is the
best Condorcet method.

"Is it possible to make a monotonic method  that's resistant to burial?"

Yes, FPP fills that bill. Other methods have  incentives to "bury" only
by truncating, not order-reversing. (According to a definition I'm not
entirely happy with this qualifiies as "burying"). I have in mind the methods
that met Later-no-Help and not Later-no-Harm, such as Bucklin and
Approval.

Chris Benham
 
 
 
 
Kristofer Munsterhjelm  wrote (Tues.Nov.25):
As we know, Smith,IRV is resistant to burial (hence my statement of "if 
you're going to have IRV, have Smith,IRV", since you gain Condorcet 
compliance). I also think Minmax-elimination is resistant to burial (at 
least it elects the "right" candidate in your Mutual Dominant Quarter 
example).

However, IRV is nonmonotonic. Is it possible to make a monotonic method 
that's resistant to burial? Dominant Mutual Third resistance? Dominant 
Mutual Quarter? It would give very unintuitive results, but might be 
needed if most of the electorate go "on a burial spree". I know of no 
method that actually has these properties, though; the method I called 
"first preference Copeland" was shown to be nonmonotonic as well 
(incidentally, by you: 
http://lists.electorama.com/pipermail/election-methods-electorama.com/2007
-January/019135.html )

(FPC is the method that, for each candidate, its penalty is the sum of 
the first preference votes of the ones that pairwise beat it. Whoever 
has least penalty wins.)



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