On Apr 14, 2010, at 7:07 AM, Kevin Venzke wrote:
Hi Juho,
--- En date de : Mar 13.4.10, Juho <juho4...@yahoo.co.uk> a écrit :
This time the
election will be arranged using WV. B supporters
note that
they can win by not supporting C any more. C
supporters do
not have the same incentive since they are about
to win.
That's only true if C voters behave on autopilot and
don't consider
the specific election they're voting in. Otherwise
they have exactly
the same incentive.
In the example I assumed that polls tell clearly that C is
more popular than B.
I'm basically saying it doesn't seem to make sense that some B
voters are
untrustworthy but all C voters are trustworthy and think B voters are
also.
Anyway I don't find this scenario compelling because while you dislike
that B voters can steal the election, you have no way of knowing that
that's what they are doing. You're going to punish everybody just to
be
safe.
In any scenario like this, some B voters will say that they honestly
did not like C.
- My assumption was that in competitive political elections all voters
may be untrustworthy if they have some easy strategy available
- It doesn't really matter whether or not B voters will tell what they
did (the problem is that they had an easy strategy available)
Maybe this is later in your mail, but I still don't
understand what you
mean by performance with sincere votes.
Simply, given sincere opinions and votes that reflect those
opinions, does the method elect the best possible
winner(s).
The fact that you don't present
any scenarios about this
I think I did. For example sincere 49: A>B, 49: C>D,
1: D>B could be one such example. WV elects D, and that
could be considered less than perfect performance with
sincere votes.
(I however think that different elections may have
different targets and therefore the best winner could be
different in different environments. For example the method
might put emphasis on finding a winner that all like a lot
on average, that is strong or that is not too much disliked
by any.)
I think you have a party list mentality. It seems like you want to
find
a winning faction, here, and pick the winner within that faction. You
see the D vote and count it to {CD}. But that's an bad idea if you're
trying to pick the candidate more representative of *all* the voters.
I don't think I wanted them to feel this way. I just assumed that in
these elections there was a clear division between "left" and
"right" (sincere in this example) (truncation would probably not be as
heavy in typical real life elections, but this example was just a
simplified example to show that WV decisions with sincere votes may
not always be what one would want them to be).
makes me believe that you consider all
truncation a strategy that would be eliminated by
margins,
Definitely I don't believe that margins would be free of
strategic temptations, and I don't think "elimination of
truncation" is any key target in margins. And in some sets
of votes margins may be worse than in WV. But margins is
somewhat more appealing to me with sincere votes. Also
(contrary to what one often hears) I don't believe that WV
would be mostly superior in the strategic scenarios.
I think it would, because a majority can truncate in an intuitive way
and gain a favorite betrayal guarantee; i.e. they can rank their
preferred
candidates however they want without making the candidate they're
united
behind lose.
Is margins better at defection scenarios? Only if it works. And I
don't
think that's realistic.
There are strategic scenarios where margins is worse (and vice versa).
Since I hope that Condorcet elections will generally allow sincere
voting I put considerable weight also on how the method performs with
sincere votes.
The
benefits of margins are maybe on its "naturalness" and in
the fact that despite of not being tailored for strategic
situations it nevertheless works quite well also in
strategic environments (maybe partly thanks to not being
fiddled in any way).
Not sure why you think this, but ok.
and so
therefore a scenario with sincere votes would be
resolved exactly the
same between WV and margins.
I didn't get this. Do you maybe mean that sincere votes
would be always fully ranked? (This would explain why you
didn't find any sincere scenarios among the WV examples that
I listed.)
I think I first asked this question before seeing your scenarios.
My claim here was that *you* probably believe that sincere votes would
always be fully ranked, which would be evidence of badness by WV every
time some ballots don't fully rank.
If you thought that, and you claim you don't, then it wouldn't be
possible
to show WV giving a bad result with sincere votes, because with
sincere
votes there would be no distinction between the two methods.
The only other thing I can think of is that you are
concerned about WV's
treatment of people who actually want to abstain from
a contest and
be counted as a schizophrenic in the margins style. In
that case I suggest
that those WV voters flip a coin to simulate the
margins treatment of
their vote.
That'd make margins and WV identical and we would not even
have to name which one of these approaches to measure
preference strength we are using.
Only with those ballots which did that.
I try not to assume
anything special on why some voters rank some candidates
equal (truncating at the end or otherwise tied elsewhere).
Technically the methods treat all reasons to rank some
candidates equal the same way (be it strategy, laziness to
rank all candidates, sincere opinion that the candidates are
equal, opinion that the candidates are close enough to equal
to rank them equal, or equality because the voter simply
does not know anything at all about those equally ranked
candidates). The explanation of the vote set may assume
something about why people voted the way they did but the
method can not (unless it contains some guidance to the
voters on how the method / organizers expect voters to vote
when they have certain feelings).
But when you "try not to assume anything special on why some voters
rank
some candidates equal (truncating at the end or otherwise tied
elsewhere)"
this leaves you no justification for your particular treatment of tied
rankings. It is not obvious to split one voter, make him vote against
himself, and *count* that to defeat strength (which is the point of
all
of this).
Of course, that is the explanation from the WV perspective.
Alternatively
you're just subtracting the vote totals. Ok, why *subtract*? Why would
the strength be based on the absolute difference of the vote totals?
It
should be the ratio surely. If you claim to not care about
abstentions from
a contest, then a 5:1 ratio should always be stronger than 4:1.
What is the "naturalness" of margins?
It's not even as easy to solve.
Yes, there could be such variants. I addressed this option shortly in
my first reply to Robert Bristow-Johnson in this chain.
I don't understand the distinction you are
making.
What I'm after is one stable explanation why the
voters
felt and voted as they did. If there are multiple
possible
explanations then I like to analyze them one by
one. The
situation that I try to avoid is one where one
feature of
the scenario will be explained using one kind of
explanation/arguments (e.g. lack of information on
the
strength of C)
I would say this is more key
and another one with another explanation
(e.g. interest not to allow third parties grow).
I can't believe I need to propose that a major party
doesn't want to help
another party to grow? One going after the same votes
even.
Yes, parties are typically competitive and want to "steal"
the votes of the others. If there is a special historical
relation between two established parties and new ones that
have earlier been unable to win and that might suffer also
now because of that legacy, this could be mentioned in the
explanation.
No there is no special relation, there is the typical relation that
you
just mentioned.
My text was not very good. The basic scenario that
I don't
like is one where multiple groups rank only the
candidates
of their own favourite group. The votes could be
100:
A1>A2>A3, 100: B1>B2>B3, 100:
C1>C2>C3
etc. WV seems to think that all candidates are
about equal
(with these votes that are at least close to
sincere) since
any additional (strategic or sincere) vote may
make any of
these candidates win. WV thus seems to ignore the
sincere
unanimous opinions/rankings within each group, and
one could
say that WV doesn't measure the opinions as one
would
expect.
I assume if you add 1 A3 vote, margins elects A1. That
strikes me as
illogical unless you're voting a party list method or
something. At
least in WV you can say that A3 might be the approval
winner.
Before the last vote A1, B1 and C1 were tied in margins.
Margins will not allow any other candidates win without a
considerable number of new votes. That last vote didn't
support A1 but it made the situation of B1 and C1 slightly
worse. They now lose to a candidate that loses a lot to A1
while earlier they didn't lose to any of the candidates.
That difference is not big but who else should be elected if
not A1? Also WV gives victory to A1 in this example (if the
additional vote was "1: A3" and not e.g. "1: A3>C2").
Ok I see. A3 has no claim over A1 just from the bullet vote. So assume
it's A3>C2. In that case according to your analysis, the A candidates
collectively beat B and C,
Only A3 beats the B and C candidates, not all A candidates, no
"collective" beating.
and then "privately" decide almost unanimously
that A1 is the candidate who should win, even though Team A wouldn't
have
won without the vote that didn't like A1 at all.
Yes, that last vote did not support A1 at all, but it was the last
straw that broke the back of B1 and C1 in margins when it made them
lose to one of the candidates (A3).
Yeah I don't like that. I'm trying to pick the most median-like
candidate,
not pick a party and then have an internal election.
All voters were free to take position on which one of the A candidates
was best. Many found them equal (or equal enough not to bother to rank
them). In a real life election B and C supporters could well agree
with this ranking. There was nothing "internal" except the common
pattern of voters truncating candidates that they do not support.
(I note that I have used term win in a sloppy way. All Condorcet
methods do not necessarily decide always the same way. I just referred
to some expected decision based on the strength of WV and margins
comparisons.)
Fundamentally we're trying to rank defeat
strengths,
not decide how to
split up votes. The WV mentality is that the
more
people that participate,
the better that information is.
Note that vote A>B=C may sometimes mean that
this voter
didn't want to participate in the B vs. C
question, but it
may as well be a clear statement that B=C.
Non-participation
may also mean that the voter wants other voters to
decide
without him/her. If we don't collect separately
information
on what the reason behind the equal rankings is we
can not
assume one way or another.
I wouldn't object so strongly to a method which
counted explicitly equal
rankings according to margins (even though this is
strategically
pointless) but truncated rankings according to WV.
Does word "truncation" carry a meaning here? (other than
the technical property of equal ranking of the last
candidates) (e.g. "ranked equal last since not approved",
"using ballots where unranked last do not have any markings,
so they can be considered not approved", "not ranked since
it was too tedious to rank them")
For me truncation means "did not evaluate because they were not good
enough." But "good enough" could be determined according to the
voter's
expectation for the election.
I should split it into two statements perhaps:
1. when people are truncating then your defensive
strategy in margins
should be to vote for the best frontrunner, because
margins won't
guarantee that a literal majority can get their way by
just voting
sincerely for the better frontrunner and everyone
thought to be better.
I hope that in large public elections people never have to
resort to defensive strategies. If people start to use
defensive strategies widely in any large public Condorcet
elections then I consider that to be a failure of the
method. I.e. the best promise of Condorcet is that it would
allow sincere voting. Strategic Condorcet would not be nice.
I don't think Condorcet can do that, and I don't think it matters.
There
isn't enough benefit:risk to trying to get complete rankings.
I'm ok with "sincere opinion", "don't care" and limited "lazy"
truncation. Only strategic use truncation ("attack" or "defence") is
something I'd like to live without (or keep it marginal). (Also
excessive "lazy" truncation (e.g. widespread "lazy" bullet voting)
would be bad.)
And strategic defensive truncation is not nice if widely
spread. That means also going towards plurality / bullet
voting.
Strategic defensive order-reversal is also not nice, and it will
lead to
plurality, at least in its results.
Yes, order reversal is also not nice.
Using defensive strategy in both WV and margins is a good idea in
general,
even with no knowledge of plans for offensive strategy. In WV it makes
offensive strategy unlikely to be reliable, and in margins it can
protect
a majority you are part of.
Widespread strategic voting could destroy the otherwise good
properties of Condorcet methods. I'd like to avoid also the use
defensive strategies.
I'm not sure if semi-controlled truncation where
some voters are expected to truncate (e.g. the ones that
expect to be the victims of a burial attack, or those who
think they are leading) while some others are expected to
vote sincerely is much nicer. And as already noted, there
may be disagreements and misunderstanding on who is supposed
and/or allowed to truncate. This approach might lead to a
big mess.
If you're talking about scenarios where one fragment of a faction is
tasked with doing one particular thing in order to steal an
election, yes,
I'm pretty sure that's a bad thing
Also defensive strategies may ruin the election (e.g. if the left wing
supporters truncate the candidates of each others).
, but no, I don't think it is a very
likely concern. And the only the fact that you're specifically talking
about truncation would make this concern favor margins over WV. I
don't
remember any reason to think that margins is harder to compromise than
WV.
I should have answered above what this means. I assume
at this point
that you have an idealized view of what would happen
when nobody ever
truncated.
I believe yes :-). I try to see Condorcet methods as a
group that in a suitable environment (very competitive but
not pathologically/irrationally competitive and not beyond
repair) would allow sincere voting as the main rule for all
rational voters.
Ok. We will have to disagree on that.
Ok, it seems I have more trust on votes staying reasonably sincere.
Condorcet methods might still be a good option in societies that can
not refrain from widespread strategic voting. What I'm afraid in WV is
that in such strategic environments the truncation based strategic
opportunities, the truncation based defensive strategy, lazy
truncation and messages like "truncated candidate = not approved
candidate" (that may lead to truncation of the main competitors) could
together lead to lots of truncation (and related problems like the
Burr dilemma).
Juho
Kevin Venzke
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