On Mon, 25 Jul 2005 10:53:52 +0300 Juho Laatu wrote:
On Jul 25, 2005, at 01:24, Dave Ketchum wrote:
"Strategically" still turns me off. Voters who preferred B over A,
and had planned to vote accordingly, are gambling that they can get
better results by claiming, instead, to prefer A over B:
In some cases they can, unfortunately, succeed at what they claim
to want.
If these can change their votes, then so can others for other
reasons, thus destroying the knowledge all used in plotting.
How cycles operate was used in the plotting. Cycles are valuable
in resolving near ties, but deliberately setting them up for intended
results is tricky.
My thoughts around the pair-wise comparison based voting methods and
strategies are roughly as follows. Rating based methods are maybe too
vulnerable to strategies in contentious elections, so we may have to
satisfy with ranking based methods. Pair-wise comparison methods are a
wonderful solution that allows voters to express their preferences quite
extensively (but still easily) and in most cases without any strategy
problems. Sincere voting thus seems to pay off (better than in many
currently used election methods). Unfortunately we have the cycle
related problems (otherwise the methods would be quite flawless).
Natural cycles are luckily quite rare. Artificially generated cycles are
a bigger problem. The big question is if pair-wise methods are still
good enough to be recommended for use. I think the differences between
different tie breaking methods are not that big. Since all of the
pair-wise comparison methods have some of the basic vulnerabilities, the
more important question seems to be if the pair-wise comparison methods
are useful in general as a group. In real election situation also the
real life environment has an influence. If majority of the voters vote
sincerely, the strategic voting problem remains just as background noise
in the process without causing any considerable harm (((hmm, the example
I presented studied the the possibility that very few strategic votes
could pick a "bad winner"...))). If the method and attitudes of voters
are bad enough, then strategic voting might be a problem. And if the
impact of strategic voting would be worse than what currently used
election methods have (e.g. some really bad candidates would be
elected), then we would need to deem pair-wise election methods unusable
(is some environments?) and would be forced to go back to (recommending)
some simpler election methods (e.g. IRV, two round runoff, plurality,
approval). So far I'm leaning in the direction that strategic voting
would at least in large public elections be marginal (or done mostly by
voters who didn't know that in the new method they don't need to vote
strategically but the a sincere vote is likely to defend their interests
in the best possible way). I'm also leaning in the direction that voting
methods that pick the best winner could be more useful than ones that
aim at eliminating strategies. Partly because people want the method to
provide best possible results, partly because the strategic fixes may be
marginal, partly to keep the method simple and understandable, and
partly because strategic countermeasures easily lead people to thinking
that strategic voting is a key property of the method. I'm not 100% sure
that the simplest methods work fine and I'm still waiting for someone to
prove that some methods are unusable and some usable (but haven't seen
(or understood :-) that yet). So, for me the question is if the basic
pair-wise comparison methods are strategy free enough to be used as
practical election methods as they are. And my guess is, yes they are in
most single winner elections.
My belief is that possibilities of strategy are best ignored, other than
preventing those who would try from having information to make them
successful.
Strategy needs both knowledge of expected results without strategy, and
cooperation among enough voters to make a difference. Assuming there is
such a group for an election, there is almost certainly room for others to
have the same vote count information, know of the first group's plotting,
and do their own plot that destroys usability of the information for the
first group.
My comparison of methods:
Condorcet wv - comparing pairs, we are looking for the most popular
candidate. When we have a near tie we call it a cycle - perhaps we could
do a runoff, but we mostly need resolution of the near tie, and all that
is needed is to break that neatly.
Condorcet margins - like above, but less apt to pick best liked.
IRV - same ballot and, almost always, same winner as above.
Sometimes fact that IRV is willing to decide without looking at whole
ballots gets bad results.
Two round runoff - expensive and, too often, best liked candidate
does not get to the runoff.
Plurality - the one thinkers want to escape.
Approval - its backers like to brag, but it is not that simple -
unlike Condorcet and IRV, voters CANNOT say: I prefer Nader but, only if
I cannot have Nader, give me Kerry as better than Bush.
Ratings - I choke on the complexity as worse than the above.
But here the example you constructed resulted in a win by the plotters
in wv - and in the result they claimed to want, but which was worse
for them than what they would have achieved without plotting, under
margins.
Yes, based on this single isolated example one should recommend margins
based methods and not winning votes based methods. I in general do like
margins also since they seem to be a more natural measure of preference
than winning votes, so this result is just fine for me :-). Winning
votes have maybe some burden of being overloaded with hopes of finding a
panacea in the fight against strategic voting.
I do not see how this example promotes margins:
Under wv the plotters achieved their goals. NOT that I approve, for
they were only guessing as to what other voters might do.
Under margins they claimed to prefer the LEAST liked candidate over
one they actually preferred. Fact that their strategy elected the least
liked is not a success to celebrate - more a warning to be cautious when
considering strategy.
Best Regards,
Juho
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Dave Ketchum 108 Halstead Ave, Owego, NY 13827-1708 607-687-5026
Do to no one what you would not want done to you.
If you want peace, work for justice.
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