[EM] Margins vs. winning-votes

[Rob LeGrand]

First, a quick point:  There are (at least) two separate issues discussed on
this list.  One is methods themselves, like Ranked Pairs vs. SSD vs. IRV vs.
Borda; this issue generates most of the interesting posts and debates.  The
other is the procedures of compiling the pairwise matrix for pairwise methods
to operate on, like margins vs. winning-votes vs. all-votes (though I don't
believe anyone still advocates all-votes).  These two issues are entirely
orthogonal-- any pairwise method can use either the margins or the
winning-votes approach, and I think Markus still prefers win-or-tie-votes for
the official definition of Schulze's Method.

Now Mike Ossipoff wants to discourage strategic truncation, but he doesn't find
it important not to encourage strategic equal rankings high in the ballot.  I
don't see truncations as anything but a specific case of equal rankings.  To
me, a vote of A>B when there are five candidates is simply a vote of A>B>C=D=E.
 I don't think this case is any more special than a case like A=B>C=D>E.  Mike
does, his favorite criteria reflect that, and that's why he prefers
winning-votes, which of course is perfectly fine for him.

What hurts a candidate most using a winning-votes method is being ranked under
another.  Being ranked equal to another hardly hurts at all.  On average,
ranking two candidates equally hurts neither.  It's good strategy to vote ties
among candidates you like and be decisive among candidates you don't.  On the
other hand, margins methods don't favor one over the other on average. 
Sometimes voting two candidates equally helps them and sometimes it hurts them,
but it always has the same expected effect as if you had flipped a coin between
them.

To me the bottom line is this:  Any evil strategy that a margins method allows
is possible in the corresponding winning-votes method, whether by flipping
coins or by coordinated bloc voting.  So, as Blake has explained, winning-votes
prevents nothing.  It only provides more strategic options for the insincere
voter, and it punishes the voter who sincerely "truncates".  I would like to
believe that winning-votes is effective, but since it's not, and margins is
more intuitive and so much better on social utility, I prefer margins.  In
fact, the false assurance that winning-votes gives its fans reminds me of my
favorite analogy of Mike's: "someone sitting in the driver's seat of a car
that's up on blocks, having fun turning the steering wheel back and forth"
(from his classic anti-IRV post
http://groups.yahoo.com/group/election-methods-list/message/6500).  Margins vs.
winning-votes is obviously a religious argument, though, so I don't expect to
change anyone's mind.  It's a bit like Newcomb's Paradox (explained at
http://www.magnolia.net/~leonf/paradox/newcomb.html), which people seem to
resolve each way in roughly equal numbers, but each group is entirely convinced
that the other is being silly.  Personally, I'd like to concentrate on newer,
more interesting debates.


=====
Rob LeGrand
honky98 at aggies.org
http://www.aggies.org/honky98/

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