[EM] Michael Rouse's letter

[MIKE OSSIPOFF]

Though I said I was qutting EM after making a few replies, I haven't
yet made those replies, and so I'm still on the list. In the meantime,
I'd like to comment briefly on this:

Michael Rouse wrote:

Although this e-mail references "Completion Methods for Smith Sets," and
they cover the same method, this is really about a stand-alone method. It
has some good qualities: it should always choose the Condorcet winner, if
there is one; if no Condorcet winner exists, it should always choose a
winner from the Smith set. It can be used in single seat and multi-seat
elections since it generates a ranking order.

I reply:

Lots of methods have those properties. One can choose from the Smith
set in many ways, of course. And, with any single-winner method, we
can get an output ranking by the following procedure:

1. Apply the count rule to the ballots to find the method's winner.
2. Delete that winner from the ballots.
3. If there are more than 1 candidate remaining on the ballots, go to 1.

The order in which candidates win is their order in the output ranking.

And so, since so many methods can meet the criteria that I quoted from
Rouse's letter, then how do we choose among all those methods? Well,
we can ask "What additional properties would you like?"

Like many others, I'd like to get rid of the lesser-of-2-evils problem.
That's the purpose of the critreria and methods described at the
website  http://www.electionmethods.org

Some methods that do a good job of that: SSD, Cloneproof SSD,
Ranked-Pairs(wv), Approval.

In fact there's a whole family of Condorcet versions that do well
by that standard. Since Condorcet wasn't very specific, it's reasonable
to say that the Condorcet methods are those methods that solve circular
ties by successively dropping defeats in a way that gives priority to
dropping weaker defeats. Some Condorcet versions other than the
ones that I listed above are: Plain Condorcet (PC) and SD. What enables
Condorcet versions to meet the criteria at the website is the use of
"defeat-support" as the measure of the strength of a defeat. If X
beats Y, the defeat-support of that defeat is the number of people who
ranked X over Y.

I realize that some here aren't interested in getting rid of the
lesser-of-2-evils problem, and they therefore have different standards
and prefer differnt methods. They aren't wrong. Standards are an
individual subjective choice. But when it's asked what properties we
want, in addition to those that Rouse named, many people, including me,
will choose the 2 standards that I named in this paragraph.

Mike Ossipoff




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