On 3/15/2013 2:12 AM, Kristofer Munsterhjelm wrote:
On 03/14/2013 06:45 PM, robert bristow-johnson wrote:
IRV will prevent a true spoiler (that is a candidate
with no viable chance of winning, but whose presence in the race changes
who the winner is) from spoiling the election, but if the "spoiler" and
the two leaders are all roughly equal going into the election, IRV can
fail and *has* failed (and Burlington 2009 is that example).
If you think about it, even Plurality is immune to spoilers... if the
spoilers are small enough. More specifically, if the "spoilers" have
less support in total than the difference in support between party
number one and two, Plurality is immune to them.
So instead of saying method X resists spoilers and Y doesn't, it seems
better to say that X resists larger spoilers than Y. And that raises the
question of how much spoiler-resistance you need. Plurality's result is
independent of very small spoilers. IRV's is of somewhat larger
spoilers, and Condorcet larger still (through mutual majority or
independence of Smith-dominated alternatives, depending on the method).
This is a good example of the need to _quantify_ the failure rate for
each election method for each "fairness" criteria.
Just a yes-or-no checkmark -- which is the approach in the comparison
table in the Wikipedia "Voting systems" article -- is not sufficient for
a full comparison.
...
It's like reinforcing a bridge that would collapse when a cat walks
across it, so that it no longer does so, but it still collapses when a
person walks across it. Cat resistance is not enough :-)
Great analogy. We need to start assessing _how_ _resistant_ each method
is to each "fairness" criteria.
It would be really useful to know what level of resistance is enough,
but that data is going to be hard to gather.[...]
Indeed, that is difficult.
> And beyond that we have even harder questions of how much resistance
> is needed to get a democratic system that works well. It seems
> reasonable to me that advanced Condorcet will do, but praxeology
> can only go so far. If only we had actual experimental data!
My VoteFair site collects lots of data. I have used it to verify that
VoteFair ranking accomplishes what it was designed to do. Not only has
such testing been useful for refining the code for the single-winner
portion (VoteFair popularity ranking, which is equivalent to the
Condorcet-Kemeny method), but such testing has revealed that VoteFair
representation ranking (which can be thought of as a two-seats-at-a-time
PR method) also works as intended.
As for praxeology ("the study of human conduct"), I also watch to see
how people try to vote strategically. The attempts are interesting, but
ineffective.
I agree that using better ballots and better vote-counting methods in
real situation -- using real data -- is essential for making real progress.
Richard Fobes
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