[EM] "Spokane" method
dfb at bbs.cruzio.com
Fri Mar 29 22:23:36 PST 1996
[p.s. Is the Spokane method actually in use? What group or person
is proposing it there?]
The Spokane method remined me, too, of Coombs, but then I noticed
a difference: Coombs repeatedly eliminates the candidate ranked last
by the most voters, but the Spokane method doesn't always do that.
For instance, after e had been eliminated, someone whose ranking
said d,a,b,e,c would have their ranking, after e's elimination, changed
to d,a,b,-,c and he's counted as giving a vote to all the candidates
but 1, and that 1 that he isn't giving a vote to is the one who's been
eliminated. That voter with that ranking _is_ counted, in that example,
as giving a vote to c, his last choice. So it's different from Coombs
if it's done just as in that example.
I haven't seem that method before, & I don't know what its properties
are yet. But I'll find out & post about it within a few days.
Don't think you're overlooking something obvious. None of us, as of
the time that I'm writing this, have studied the details of the
results of that method, but there's nothing obvious that we've
If the guy _did_ mean to just repeatedly eliminate the candidate who's
the last choice of the most voters, that's one of the best non-pairwise
methods. I consider it 1 of the 2 best non-pairwise methods. The other
is too complicated to justify its consideration, especially since it
isn't nearly as good as Condorcet's method.
If one wants to do an elimination method, instead of a pairwise method,
it's better to go by last choices than 1st choices.
The trouble with Coombs is that the progressives, for instance, might
be split about whom they rank last, among the candidates that they
rank. This could cause a split-vote for last choice, which could
cause last choices to be eliminated from the progressive side
consistently, eating away the whole set of candidates from the
I consider that to not be as bad as MPV's split-vote problem,
because it's easier for the progressives to artificially agree
on how to order their really low choices than it would be for
them all to like to insincerely rank someone 1st, as MPV might
require them to do.
I don't recommend Coombs because the kind of strategy that it
needs, agreeing on lower choices, is unfamiliar to voters, and
the method could fail for that reason. I much prefer a really
strategy-free method like Condorcet.
But, though I don't recommend it for that reason, & because Condorcet
isn't appreciably more complicated anyway, and is strategy-free under
ordinary conditions, and, even under the worst conditions, its
defensive strategy isn't unfamiliar--even so, Coombs has the appeal
that, if, for instance, the progressives can agree on how to order
the lowest candidates they rankk (& of course they need only rank
candidates who have a chance of being Condorcet winner, a needed
compromise), then the method works very well: With a 1-dimensional
political spectrum, the last choices are going to be the extremes.
Everone's last choice will be 1 of the 2 extremes. So Coombs naturally
nibbles from the extreme ends of the spectrum till only the Condorcet
winner is left. But I believe that Coombs's strategy requirement
disqualifies it from being as good as Condorcet, and convincingly
argues against proposing it to the public, or any group taking a vote,
when the better Condorcet's method is available.
Though I haven't studied Coombs for a while, it seems to me that
it did ok against truncation, subject to the condition that people
avoid split-vote for last choice by agreeing on low choices, but that
it did require extra strategy to defend against order-reversal.
A defensive strategy more unfamiliar than that of Condorcet under
those conditions, in addition to the need to agree on low choice
orderings. Like I said, I don't recommend Coombs' method.
I want to say that what's been called the Generalized Majority
Criterion should, in my opinion, be called the Mutual Majority Criterion,
because it isn't really general. More about that soon, tonight or
early tommorow morning. Briefly, I want it to be possible for a
majority of the voters to get what they want without ranking
a less-liked alternative equal to or over a more-liked one, or,
under specified conditions, using any kind of strategy at all.
The Mutual Majority Criterion overlooks some important violations
of that wish. More later.
I have another criterion that I'd call the Generalized Majority
Criterion. It's unashamedly tailored to what seems possible to get
with single-winner methods, and it's wordy to express. It's
a yes/no test based on the generalized majority standard that
I described earlier. More about that tonight or early tomorrow
Also, I'll be checking out the properties of the Spokane method,
as defined by that example. I don't yet know what its properties
are. Someone might point out that there's a simple way of
saying what it does. Someone might point that out before I do.
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