Re: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Some of the replies are taking the subject line too literally. We're not
talking about top two runoff, but two member PR runoff. we find out who
the two member parliament would be then pit those two against each other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C is
the second member.
The runoff is between A and C, not between A and B, as some people are
assuming.
If the B faction defects, then the two members of the pariliament would be
B and C, and the pairwise winner would be B, so the method does not satisfy
CD.
Date: Thu, 10 Nov 2016 22:21:07 +0000 (UTC)
From: Kevin Venzke stepjak@yahoo.fr
To: Monkey Puzzle araucaria.araucana@gmail.com, EM
election-methods@lists.electorama.com
Subject: Re: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Message-ID: 610944053.3025054.1478816467543@mail.yahoo.com
Content-Type: text/plain; charset="utf-8"
Hello,
I'm mainly saying that (purely in theory) the runoff method shouldn't
behave any differently from Approval (i.e. if the nominators know what they
are doing and voters don't mind clones). I don't see an advantage to having
the voters pick between two clones when (in theory, again) those clones
wouldn't even be there, save for the incentives of the method. You could
counter my criticism by saying a mechanism is allowed to be "theoretically"
pointless if in practice it would be OK. Harder to sell such a method
though, I think.
The method doesn't satisfy Participation or IIA. Notice that deleting the
loser of the final runoff does not necessarily preserve the original
winner. And adding ballots that approve the winner can change who the
winner is up against, making him lose.
Kevin
De?: Monkey Puzzle <araucaria.araucana@gmail.com>
??: EM election-methods@lists.electorama.com
Envoy? le : Jeudi 10 novembre 2016 13h31
Objet?: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Back in 2005, Russ Paielli proposed the following to this list:(
https://www.mail-archive.com/election-methods-
electorama.com@electorama.com/msg06164.html)
I'm up too late again, and I just had an interesting idea. If the
following method has been proposed before, please let me know.
The voters rank the candidates and specify an Approval cutoff. The
winner is then the pairwise winner of the top-two most-approved candidates.
If it doesn't have a name already, let me tentatively call it ATTPR for
Approval Top-Two Pairwise Runoff.
A simpler variation would be to let the voter rank only the approved
candidates, thereby eliminating the need for an explicit Approval cutoff.
Good night, or good morning, whichever the case may be.
I'd like to revive this proposal, in the following form, still basically
what Russ proposed:
Voters grade the candidates on a 6 level scale, A>B>C>D>E>F.
Grades A, B, or C are approved; D, E, or F are disapproved.
Rank preferences are inferred from ratings, and the pairwise winner of the
top two approved candidates is the winner.
I'd like to defend this method against the two objections posed at the
time:
Kevin Venzke raised the following objection:
This fails Clone-Loser pretty badly: if the faction commanding the most
approval runs two candidates, they can win regardless of the pairwise
comparison.
My take on this is that you would have the same problem with straight
Approval. ? The full pairwise comparison ensures that the least
objectionable of the clones (to both winning and losing factions) is the
one who wins.? Since my primary metric is finding the candidate who
minimizes variance, there is better variance-minimizing when those
disagreeing with the top-two approved candidates are able to have a voice
in the comparison between the two.
Chris Benham responded with the following objection:
This would be a strategy farce. Voters who are only interested in
electing their favourite would all have incentive to approve, besides
their favourite, any and all candidates
that they think that their favourite can beat in the runoff. The net
effect of this strategising could be that that the two candidates in
the runoff could be the two least popular
(sincerely approved).
As well of course, as Kevin pointed out, well-resourced parties would
have incentive to each run two candidates to try to capture both runoff
spots.
I disagree with the supposed strategic incentive.? This seems to be a
combination of pushover strategy plus Chicken Dilemma.? The very fact that
one might promote more than one sincerely disapproved candidate into the
top-two set is itself a disincentive to the attempt, since you get only one
coarse-grained shot at the top two.? I think pairwise runoff is an
incentive to avoid CD, but possibly not.
And again, I'm not worried about a runoff between clones.? The advantage
of TTA is that if the larger faction is going to win anyway, the losing
factions can at least have a voice in deciding the lesser of two evils.
I'm primarily concerned about participation, monotonicity and independence
from irrelevant alternatives.? It seems to me that participation is
satisfied as it would be with straight approval, since adding an approved
vote for your favorite would never decrease approval, and adding a
preference between favorite and any other compromise should never hurt
either favorite or compromise. ?
IIA seems like it should be satisfied because adding or removing a
non-top-two candidate should never have an effect on the top-two pairwise
comparison.
The latter is interesting to me because one would expect that a method
with ranking would fall under Arrow Impossibility conditions.
It is apparent that TTAPR can fail Condorcet when the sincere CW is not in
the top-two approved, but there is less chance of that occurring than would
happen in simple Approval, so I see an improvement.? Of course, it would
still fail Smith and other full set Condorcet criteria also.
In an ideal world, I would like to reduce the weight of the pairwise vote
between two disapproved candidates, but in a USA-type election, it seems
like one has to ensure that ballot weight is always 1 when making candidate
comparisons to satisfy constitutional requirements.
Finally, I think this satisfies all the monotonicity criteria satisfied by
Approval.? Are there any counterexamples?
Ted--??Frango ut patefaciam -- I break so that I may reveal
The very first post quoted and responded to me talking about TTAPR. Thus you get a response about TTAPR
I do understand how this PR method works.
Kevin
De : Forest Simmons <fsimmons@pcc.edu>
À : EM election-methods@lists.electorama.com
Envoyé le : Jeudi 10 novembre 2016 18h48
Objet : Re: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Some of the replies are taking the subject line too literally. We're not talking about top two runoff, but two member PR runoff. we find out who the two member parliament would be then pit those two against each other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C is the second member.
The runoff is between A and C, not between A and B, as some people are assuming.
If the B faction defects, then the two members of the pariliament would be B and C, and the pairwise winner would be B, so the method does not satisfy CD.
Date: Thu, 10 Nov 2016 22:21:07 +0000 (UTC)
From: Kevin Venzke stepjak@yahoo.fr
To: Monkey Puzzle araucaria.araucana@gmail.com , EM
<election-methods@lists. electorama.com>
Subject: Re: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Message-ID: <610944053.3025054. 1478816467543@mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"
Hello,
I'm mainly saying that (purely in theory) the runoff method shouldn't behave any differently from Approval (i.e. if the nominators know what they are doing and voters don't mind clones). I don't see an advantage to having the voters pick between two clones when (in theory, again) those clones wouldn't even be there, save for the incentives of the method. You could counter my criticism by saying a mechanism is allowed to be "theoretically" pointless if in practice it would be OK. Harder to sell such a method though, I think.
The method doesn't satisfy Participation or IIA. Notice that deleting the loser of the final runoff does not necessarily preserve the original winner. And adding ballots that approve the winner can change who the winner is up against, making him lose.
Kevin
De?: Monkey Puzzle araucaria.araucana@gmail.com
??: EM <election-methods@lists. electorama.com>
Envoy? le : Jeudi 10 novembre 2016 13h31
Objet?: [EM] Top-two Approval Pairwise Runoff (TTAPR)
Back in 2005, Russ Paielli proposed the following to this list:(https://www.mail- archive.com/election-methods- electorama.com@electorama.com/ msg06164.html)
I'm up too late again, and I just had an interesting idea. If the
following method has been proposed before, please let me know.
The voters rank the candidates and specify an Approval cutoff. The
winner is then the pairwise winner of the top-two most-approved candidates.
If it doesn't have a name already, let me tentatively call it ATTPR for
Approval Top-Two Pairwise Runoff.
A simpler variation would be to let the voter rank only the approved
candidates, thereby eliminating the need for an explicit Approval cutoff.
Good night, or good morning, whichever the case may be.
I'd like to revive this proposal, in the following form, still basically what Russ proposed:
Voters grade the candidates on a 6 level scale, A>B>C>D>E>F.
Grades A, B, or C are approved; D, E, or F are disapproved.
Rank preferences are inferred from ratings, and the pairwise winner of the top two approved candidates is the winner.
I'd like to defend this method against the two objections posed at the time:
Kevin Venzke raised the following objection:
This fails Clone-Loser pretty badly: if the faction commanding the most
approval runs two candidates, they can win regardless of the pairwise
comparison.
My take on this is that you would have the same problem with straight Approval. ? The full pairwise comparison ensures that the least objectionable of the clones (to both winning and losing factions) is the one who wins.? Since my primary metric is finding the candidate who minimizes variance, there is better variance-minimizing when those disagreeing with the top-two approved candidates are able to have a voice in the comparison between the two.
Chris Benham responded with the following objection:
This would be a strategy farce. Voters who are only interested in
electing their favourite would all have incentive to approve, besides
their favourite, any and all candidates
that they think that their favourite can beat in the runoff. The net
effect of this strategising could be that that the two candidates in
the runoff could be the two least popular
(sincerely approved).
As well of course, as Kevin pointed out, well-resourced parties would
have incentive to each run two candidates to try to capture both runoff
spots.
I disagree with the supposed strategic incentive.? This seems to be a combination of pushover strategy plus Chicken Dilemma.? The very fact that one might promote more than one sincerely disapproved candidate into the top-two set is itself a disincentive to the attempt, since you get only one coarse-grained shot at the top two.? I think pairwise runoff is an incentive to avoid CD, but possibly not.
And again, I'm not worried about a runoff between clones.? The advantage of TTA is that if the larger faction is going to win anyway, the losing factions can at least have a voice in deciding the lesser of two evils.
I'm primarily concerned about participation, monotonicity and independence from irrelevant alternatives.? It seems to me that participation is satisfied as it would be with straight approval, since adding an approved vote for your favorite would never decrease approval, and adding a preference between favorite and any other compromise should never hurt either favorite or compromise. ?
IIA seems like it should be satisfied because adding or removing a non-top-two candidate should never have an effect on the top-two pairwise comparison.
The latter is interesting to me because one would expect that a method with ranking would fall under Arrow Impossibility conditions.
It is apparent that TTAPR can fail Condorcet when the sincere CW is not in the top-two approved, but there is less chance of that occurring than would happen in simple Approval, so I see an improvement.? Of course, it would still fail Smith and other full set Condorcet criteria also.
In an ideal world, I would like to reduce the weight of the pairwise vote between two disapproved candidates, but in a USA-type election, it seems like one has to ensure that ballot weight is always 1 when making candidate comparisons to satisfy constitutional requirements.
Finally, I think this satisfies all the monotonicity criteria satisfied by Approval.? Are there any counterexamples?
Ted--??Frango ut patefaciam -- I break so that I may reveal
Election-Methods mailing list - see http://electorama.com/em for list info
On 11/11/2016 01:48 AM, Forest Simmons wrote:
Some of the replies are taking the subject line too literally. We're
not talking about top two runoff, but two member PR runoff. we find out
who the two member parliament would be then pit those two against each
other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C is
the second member.
The runoff is between A and C, not between A and B, as some people are
assuming.
If the B faction defects, then the two members of the pariliament would
be B and C, and the pairwise winner would be B, so the method does not
satisfy CD.
On a more intuitive level, that isn't too surprising. Suppose you have a
Bush-Nader-Gore situation. The runoff doesn't help the voters who want
to know whether to vote {Nader, Gore} or {Nader}, since if they vote
only Nader, Bush and Gore may go to the runoff (i.e. Nader loses). On
the other hand, if they do vote {Nader, Gore}, and Gore is picked for
the first winner, then their ballots will be deweighted and Nader
probably won't come in second anyway.
In this chicken dilemma defection situation, the As and Bs could add
preferences below the approval cutoff:
40 C
32 A>>B
28 B>>A
Both groups defect from each other, but assign their rival a higher
preference above other disapproved candidates.
C and the larger first choice of A or B are the two parliament seats, and
the disapproved preference helps that candidate win.
Frango ut patefaciam -- I break so that I may reveal
On Fri, Nov 11, 2016 at 12:21 AM, Kristofer Munsterhjelm <
km_elmet@t-online.de> wrote:
On 11/11/2016 01:48 AM, Forest Simmons wrote:
Some of the replies are taking the subject line too literally. We're
not talking about top two runoff, but two member PR runoff. we find out
who the two member parliament would be then pit those two against each
other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C is
the second member.
The runoff is between A and C, not between A and B, as some people are
assuming.
If the B faction defects, then the two members of the pariliament would
be B and C, and the pairwise winner would be B, so the method does not
satisfy CD.
On a more intuitive level, that isn't too surprising. Suppose you have a
Bush-Nader-Gore situation. The runoff doesn't help the voters who want
to know whether to vote {Nader, Gore} or {Nader}, since if they vote
only Nader, Bush and Gore may go to the runoff (i.e. Nader loses). On
the other hand, if they do vote {Nader, Gore}, and Gore is picked for
the first winner, then their ballots will be deweighted and Nader
probably won't come in second anyway.
Election-Methods mailing list - see http://electorama.com/em for list info
Very good! And it works for a variety of Proportional Representation
methods, whether you deweight the ballots to 1/2, 1/3, or even totally
deweight to zero, so that no ballot that approved the first finalist has
any weight at all in deciding who the second finalist is. That may be the
simplest method.
On Fri, Nov 11, 2016 at 10:13 AM, Monkey Puzzle <
araucaria.araucana@gmail.com> wrote:
In this chicken dilemma defection situation, the As and Bs could add
preferences below the approval cutoff:
40 C
32 A>>B
28 B>>A
Both groups defect from each other, but assign their rival a higher
preference above other disapproved candidates.
C and the larger first choice of A or B are the two parliament seats, and
the disapproved preference helps that candidate win.
Frango ut patefaciam -- I break so that I may reveal
On Fri, Nov 11, 2016 at 12:21 AM, Kristofer Munsterhjelm <
km_elmet@t-online.de> wrote:
On 11/11/2016 01:48 AM, Forest Simmons wrote:
Some of the replies are taking the subject line too literally. We're
not talking about top two runoff, but two member PR runoff. we find out
who the two member parliament would be then pit those two against each
other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C is
the second member.
The runoff is between A and C, not between A and B, as some people are
assuming.
If the B faction defects, then the two members of the pariliament would
be B and C, and the pairwise winner would be B, so the method does not
satisfy CD.
On a more intuitive level, that isn't too surprising. Suppose you have a
Bush-Nader-Gore situation. The runoff doesn't help the voters who want
to know whether to vote {Nader, Gore} or {Nader}, since if they vote
only Nader, Bush and Gore may go to the runoff (i.e. Nader loses). On
the other hand, if they do vote {Nader, Gore}, and Gore is picked for
the first winner, then their ballots will be deweighted and Nader
probably won't come in second anyway.
Election-Methods mailing list - see http://electorama.com/em for list
info
The "deweight to zero" option would be best for avoiding an extra easy
Push-over incentive.
With voters being allowed to rank both above and below an approval
threshold, this a one-ballot per voter and one trip
to the polling station version of an earlier suggestion of mine for a 2
trips to the polling station method using simple Approval
ballots.
But then we have a method that can badly fail Condorcet and fails FBC.
I suppose if we don't mind a kludge fix it to meet Condorcet:
Voters submit rankings with an approval threshold (Default is all
candidates ranked above equal-bottom are interpreted as approved).
Elect the CW if there is one.
Otherwise elect the pairwise winner between (among members of the Smith
set?) the most approved candidate A and the candidate
most approved on ballots that don't approve A.
Chris Benham
On 11/12/2016 10:51 AM, Forest Simmons wrote:
Very good! And it works for a variety of Proportional Representation
methods, whether you deweight the ballots to 1/2, 1/3, or even totally
deweight to zero, so that no ballot that approved the first finalist
has any weight at all in deciding who the second finalist is. That
may be the simplest method.
On Fri, Nov 11, 2016 at 10:13 AM, Monkey Puzzle
<araucaria.araucana@gmail.com mailto:araucaria.araucana@gmail.com>
wrote:
In this chicken dilemma defection situation, the As and Bs could
add preferences below the approval cutoff:
40 C
32 A>>B
28 B>>A
Both groups defect from each other, but assign their rival a
higher preference above other disapproved candidates.
C and the larger first choice of A or B are the two parliament
seats, and the disapproved preference helps that candidate win.
Frango ut patefaciam -- I break so that I may reveal
On Fri, Nov 11, 2016 at 12:21 AM, Kristofer Munsterhjelm
<km_elmet@t-online.de <mailto:km_elmet@t-online.de>> wrote:
On 11/11/2016 01:48 AM, Forest Simmons wrote:
Some of the replies are taking the subject line too
literally. We're
not talking about top two runoff, but two member PR runoff.
we find out
who the two member parliament would be then pit those two
against each
other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in
half, so C is
the second member.
The runoff is between A and C, not between A and B, as some
people are
assuming.
If the B faction defects, then the two members of the
pariliament would
be B and C, and the pairwise winner would be B, so the
method does not
satisfy CD.
On a more intuitive level, that isn't too surprising. Suppose
you have a
Bush-Nader-Gore situation. The runoff doesn't help the voters
who want
to know whether to vote {Nader, Gore} or {Nader}, since if
they vote
only Nader, Bush and Gore may go to the runoff (i.e. Nader
loses). On
the other hand, if they do vote {Nader, Gore}, and Gore is
picked for
the first winner, then their ballots will be deweighted and Nader
probably won't come in second anyway.
----
Election-Methods mailing list - see http://electorama.com/em
for list info
Election-Methods mailing list - see http://electorama.com/em for list info
Chris's suggestion is a good one, though in some ways the original idea has
come full circle.
His suggestion is now reduced to a form of Condorcet completion.
The primary difference from Smith//Approval is that unless the Smith Set is
explicitly required, the winner could potentially come from outside the
Smith Set.
In the example below,
40 C
32 A >> B
28 B >> A
A is the CW and the completion rule is not necessary. But I can imagine
that there might be situations where a determined CD betrayal by B voters
could force the approval two-seat parliament runoff and prevent A from
being one of the contenders.
Frango ut patefaciam -- I break so that I may reveal
On Fri, Nov 11, 2016 at 11:18 PM, C.Benham cbenham@adam.com.au wrote:
The "deweight to zero" option would be best for avoiding an extra easy
Push-over incentive.
With voters being allowed to rank both above and below an approval
threshold, this a one-ballot per voter and one trip
to the polling station version of an earlier suggestion of mine for a 2
trips to the polling station method using simple Approval
ballots.
But then we have a method that can badly fail Condorcet and fails FBC.
I suppose if we don't mind a kludge fix it to meet Condorcet:
Voters submit rankings with an approval threshold (Default is all
candidates ranked above equal-bottom are interpreted as approved).
Elect the CW if there is one.
Otherwise elect the pairwise winner between (among members of the Smith
set?) the most approved candidate A and the candidate
most approved on ballots that don't approve A.
Chris Benham
On 11/12/2016 10:51 AM, Forest Simmons wrote:
Very good! And it works for a variety of Proportional Representation
methods, whether you deweight the ballots to 1/2, 1/3, or even totally
deweight to zero, so that no ballot that approved the first finalist has
any weight at all in deciding who the second finalist is. That may be the
simplest method.
On Fri, Nov 11, 2016 at 10:13 AM, Monkey Puzzle <
araucaria.araucana@gmail.com> wrote:
In this chicken dilemma defection situation, the As and Bs could add
preferences below the approval cutoff:
40 C
32 A>>B
28 B>>A
Both groups defect from each other, but assign their rival a higher
preference above other disapproved candidates.
C and the larger first choice of A or B are the two parliament seats, and
the disapproved preference helps that candidate win.
Frango ut patefaciam -- I break so that I may reveal
On Fri, Nov 11, 2016 at 12:21 AM, Kristofer Munsterhjelm <
km_elmet@t-online.de> wrote:
On 11/11/2016 01:48 AM, Forest Simmons wrote:
Some of the replies are taking the subject line too literally. We're
not talking about top two runoff, but two member PR runoff. we find
out
who the two member parliament would be then pit those two against each
other.
So
40 C
32 A>B
28 B>A
Suppose that we use PAV with implicit approval
The A is the first member in the two member parliament.
The two factions that supported A get their weights cut in half, so C
is
the second member.
The runoff is between A and C, not between A and B, as some people are
assuming.
If the B faction defects, then the two members of the pariliament would
be B and C, and the pairwise winner would be B, so the method does not
satisfy CD.
On a more intuitive level, that isn't too surprising. Suppose you have a
Bush-Nader-Gore situation. The runoff doesn't help the voters who want
to know whether to vote {Nader, Gore} or {Nader}, since if they vote
only Nader, Bush and Gore may go to the runoff (i.e. Nader loses). On
the other hand, if they do vote {Nader, Gore}, and Gore is picked for
the first winner, then their ballots will be deweighted and Nader
probably won't come in second anyway.
Election-Methods mailing list - see http://electorama.com/em for list
info
Election-Methods mailing list - see http://electorama.com/em for list info
Election-Methods mailing list - see http://electorama.com/em for list info