On May 7, 2010, at 6:13 PM, Kevin Venzke wrote:
Hi Juho,
--- En date de : Ven 7.5.10, Juho <[email protected]> a écrit :
Another characteristic feature of the Schulze method is the
use of winning votes. My understanding is that the history
behind winning votes is mostly based on strategic voting
related concerns. Unless use of winning votes is considered
ideal for sincere votes, this decision means some deviation
from electing ideal winners wit sincere votes.
Yet another possible factor that may influence this
discussion on what the basic idea behind Schulze method (and
other methods) is is the concept of implicit approval cutoff
after the ranked candidates. Some criteria and discussion on
what the ideal winner is do refer to the assumption that
voters have indicated that they support/approve those
candidates that they have ranked and do not support
candidates that they have not ranked. (Depending on the
ballot type and number of candidates and interpretation that
could mean truncation or candidates ranked equal last.) This
interpretation of the votes is thus not purely ranking based
but includes also additional information. One problem of
this approach is that if voters behave this way then will
not express their preferences on the preference between
those candidates that they do not like, and that could mean
high level of truncation and bullet voting. Implicit
approval argumentation usually appears together with
arguments on why winning votes are natural or how they
work.
My understanding of the history of developments behind the
Schulze method is that in addition to Condorcet
compatibility one has aimed at summable matrix, 100%
independence of clones, defence against some strategic
voting patterns (=> winning votes), deterministic
decisions (best candidate elected, no lotteries, except when
exact ties). I don't think the interest to aim at minimum
number of ballots that must be eliminated (or added) has
been a key target, at least not the leading one. The
strategic concerns must have been strong if one considers
winning votes not to be optimal with sincere votes.
*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.)
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.
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.
Juho
The main difference between Schulze and RP is a preference
to ignore small defeats over trying to make a ranking by locking
larger
defeats.
Kevin Venzke
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