[EM] MDDA vs UncAAO, ASM & DMC
mikeo2106 at msn.com
Sun Mar 11 10:11:49 PDT 2007
UncAAO, ASM, and DMC ignore defeat-magnitude and magnitude of pair-wise
opposition. They look at pair-wise vote totals in order to find out who
beats whom, but then they throw pair-wise vote total information away.
Throwing that information away has regrettable consequences.
Making use of pairwise defeat magnitudes is a two edged sword. Yes, it gives
information, but it also gives incentive for voters to go out of their way
to add more to the defeat strengths that they feel a strategic need for even
when the defeat itself is already assured.
Substituting Approval measures of defeat strength allows for strategic
control without requiring order reversal or collapse.
But strategy is then more often needed than with MDDA, MAMPO or wv
I have nothing against Approval, but relying on it to measure
defeat-strength brings Approvals strategy need to rank methods. Rank
methods could offer more than that.
Offensive order-reversal works in DMC too. If theres less incentive for it,
its because truncation works just as well in DMC. DMC is vulnerable to
truncation in a sense that MDDA, MAMPO and wv Condorcet are not, as examples
below will demonstrate.
You spoke of incentive for order-reversal. Im more interested in strategic
_need_ for order-reversal. That need is at its worst when a voter needs to
bury his favorite in order to keep a greater-evil from winning, to protect
majority rule, or to protect a CW. That need will never exist with MDDA or
MAMPO. But it will with DMC. There are numerous possible examples.
51: AC (offensive order-reversal)
50: C/B (/ denotes approval cutoff)
The A voters have made a cycle, and, B, being least approved, is eliminated,
and A wins.
But if one C voter voted B over C, then B would win its pair-wise comparison
with C, and so B would win the count.
All of the truncation examples that follow are also FBC failure examples,
since one C voter could reverse the C>B defeat by voting B over C.
As I said, DMC has a problem with truncation, where MDDA, MAMPO, and wv
Condorcet do not:
The A voters truncation causes a cycle. B again has the least approval and
is eliminated, electing A.
As before, one C voter could save the CW, enforce majority rule, and defeat
a greater-evil by voting B over his/her favorite.
I emphasize that the need for favorite burial is nonexistent in MDDA and
You can object that the above problem happens because the C voters didnt
approval B. Sure, but thats the point: Strategy use is needed to enforce
majority rule, protect the CW, and prevent the election of the greater-evil.
That isnt so with MDDA, MAMPO or wv Condorcet. With those methods the B
voters and C voters need do nothing other than rank sincerely, in order to
keep A from winning. For that reason, MDDA, MAMPO and wv Condorcet fulfill
the full promise of rank balloting.
This time, with the B voters helping A, even two A voters can steal the
election from the CW by truncation. Yes, the B voters and C voters could use
better approval strategy, thereby saving the CW, enforcing majority rule,
and preventing the election of a greater-evil.. But, as I said, thats the
whole point: They need to use the right approval strategy. In MDDA, MAMPO
and wv Condorcet, they dont need any strategy at all. They need only rank
sincerely, and its guaranteed by SFC compliance that A cant win.
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