On Apr 15, 2009, at 8:20 AM, Kristofer Munsterhjelm wrote:
Jonathan Lundell wrote:
C wins by 70/93 = 75.3% of the votes. What a landslide!
(Schulze and MAM gives A > D > C > B, and IRV gives A > B > C = D.)
That's really a mischaracterization of IRV. IRV (and STV in
general) does not produce a candidate ordering. It simply finds a
winner by interpreting the ballots as a list of contingent choices.
In particular, no ranking is implied by order of elimination.
Alright. The point of the ordering was to show that the elimination
method of "eliminate whoever got the most Plurality votes" is rather
bad, and also that it produces a different result than IRV. Schulze
and MAM agrees that C is the next worst candidate, and IRV (like
Schulze and MAM) elects A as the winner.
Let's call the method of my previous post "Worst Runoff". Worst
Runoff, like all single-elimination methods, passes Condorcet Loser
- so there's no way to get it to elect B.
Whether or not IRV produces an ordering is not really important.
What is important is that you can stretch the "elected by a
majority" definition to apply to any elimination system - at least
unless you provide the caveat of "assuming the voters know what the
method does, so that when they submit ranked ballots, they
implicitly consent to the method's treatment of those ballots". If
one uses this qualification, then IRV's property of "elects what a
majority of the voters want" is either incorrect (because the voters
don't "know what the method does" to the intuitive level required)
or is a near-tautology (as any method that takes a majority of the
ballots into account would satisfy this criterion).
I agree to this extent: "majority" is a fuzzy concept, and in any
particular application it needs to be precisely defined.
I think it's easy enough to phrase IRV voting instructions in terms of
contingency, though I don't think it's particularly harmful for voters
to think of their ballot as a simple preference ordering, because the
likelihood that a voter will have sufficient information to make it
worthwhile to vote strategically is vanishingly small, at least in
real public elections.
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