On May 8, 2010, at 6:32 AM, Kevin Venzke wrote:
Hi Juho,
--- En date de : Ven 7.5.10, Juho <[email protected]> a écrit :
*Who* must have considered winning votes to not be
optimal with sincere
votes?
I don't really know what others have thought. My first
approach when I first time thought about pairwise comparison
based methods was that margins would be a natural and simple
way to measure preference strengths, and I needed an
explanation to why one would use wining votes. The
argumentation that I found was related to strategic voting.
Never mind that you noticed above that WV advocates
tend to have a
different conception of truncation. (Though I wouldn't
call it
disapproval; disapproval is likely, but the point is
abstention.)
The arguments I remember are about majorities and
sincere CWs more than
about fixing strategic incentives for its own sake.
There have been arguments that the reason why margins is
not good is its strategic vulnerabilities when compared to
winning votes. (This means that winning votes have been
considered to be better because of strategy related reasons.
But this doesn't say anything on if someone finds winning
votes to be ideal with sincere votes.)
And it doesn't say anything on whether someone finds margins to be
ideal
with sincere votes.
It's just me and some others that have said that margins seems at
least more natural than winning votes (not necessarily ideal).
What *does* mean that WV is considered to be better with sincere votes
is the perspective that when voters truncate they mean to abstain, and
not lend weight to the ignored contests.
What does "abstain" mean? Margins thinks that 40-30 and 30-20 opinions
are of same strength. Should we consider the strengths of those
opinions to be (40-30)/70 and (30-20)/50? Now we treat the truncated
and equal rankings in some sense as abstentions. This approach has
also been discussed but it is not winning votes. With this approach
opinion 30-20 is stronger than 40-30 (unlike in winning votes). It
differs from margins in that it counts how much stronger the winning
side is in percentage (not in number of votes as in margins).
I don't have any better explanations to winning votes as the ideal way
to measure preference strengths (better than "number of votes on the
winning side against some other candidate").
FPP has strategic problems beyond those found in
IRV... We don't conclude
from this that FPP is better with sincere votes. We
don't take arguments
about FPP's strategic problems as an admission that
"otherwise" (???) FPP
was just fine.
Why couldn't I say that the point of *margins* is to
minimize a strategic
incentive?
There are cases where margins are less vulnerable to
strategic voting than winning votes but I don't recall
anyone saying that margins would have been designed with
this in mind.
I'm talking about truncation here, and the way margins makes it
useless.
I think the margins philosophy is that truncations and equal rankings
are both treated as equal rankings. Or do you mean that truncation
should be interpreted as some kind of "implicit approval cutoff"?
Should "A=B>C" be treated differently than "C>A=B" or "C" with respect
to the pairwise comparison between A and B? Or do you refer to
truncation as a strategic defence mechanism?
My point is more that I don't know of any coherent explanation of why
margins is "ideal" with sincere votes, and WV is not. But that
explanation
must be out there if the only problem WV advocates have with margins
is
its strategic incentives. There must be some 10+-year-old posts from
WV
advocates unhappy that they can't just use margins.
There are many mails and web articles. But maybe less on the
performance with sincere votes than about strategies. At least
according to my experience it is difficult to raise good quality
discussion on that very central topic.
Considering that you just complained about the
potential
strategic implications of the WV view of truncation.
I mentioned at least the possibility of message "truncation
= approval" possibly leading to shorter than fully ranked
votes.
Schulze and WV are only not focused on minimizing the
number of
"eliminated" ballots in the narrow sense that you pick
out to support
margins. Practically the whole point of WV is to be
able to ignore the
smallest number of preferences that were actually
specified, rather than
imagined.
With 100 voters opinion 40-30 means that there are 30
no-opinions or equal opinions. Margins seems to assume that
the (from 0 to 30) no-opinions are either equal opinions or
50%-50% in both directions. One could also assume that every
truncated vote and vote that contains equal rankings is
intentionally created by the voter and therefore the voter
intentionally wants these candidates to be considered equal.
Winning votes seems to assume that no-opinion and equal
opinion correspond to voting against the pairwise winner
since 40-30 and 40-0 have the same meaning.
That is ridiculous. What can "correspond" mean when adding votes
against
the pairwise winner can make him the pairwise loser?
Yes, the rules are asymmetric in the sense that the description of the
strength of the defeat changes depending on which one of the
candidates wins.
I guess what you mean to point out is that WV actually does ignore a
type of preference actually expressed. Fair enough, but it doesn't
matter
to my point, which is just that WV actually does have logic that has
a resemblance to - and is as completely arbitrary on a purely
aesthetic
level as - the principle of adding/removing as few ballots as
necessary
to create a CW.
I wonder if someone has somewhere written a description on how winning
votes is intended to measure sincere opinions.
Juho
P.S. My biggest fears with winning votes is that it might in some real
elections (with sincere votes) produce a result that people do not
find natural.
10: A>B=C
20: A>B>C
16: A>C>B
01: B>A=C
01: B>A>C
26: B>C>A
03: C>A=B
03: C>A>B
20: C>B>A
This set of votes is cyclic. B and C are from the same wing (they
support each others). But should C win (as in most methods with
winning votes) although B has more first preferences than C and also A
supporters like B more than C?
Kevin Venzke
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