[EM] Scoring (was Re: OpenSTV 2.1.0 released)

Michael Ossipoff email9648742 at gmail.com
Mon Sep 24 23:31:08 PDT 2012


Here's the MinMax(margins) chicken dilemma example that I promised, in
which defection by B voters is successful and rewarded::

Sincere preferences:

75: A>B>>C
51: B>A>>C
100: C>>(A=B)

Voted rankings:

75: A>B
51: B
100: C

Try MinMax(margins) with that example.

Note that it's a Dodgson example too.

Note also that the B faction is small in comparison to the other factions.

Condorcet(wv) reliably rewards defection.

SITC reliably thwarts and penalizes defection.

Though MinMax(margins) and Dodgson don't reward defection quite as
reliably as does wv, (though the example shows that they easily do
so), they certainly don't reliably thwart and penalize it either.

An additional problem of MinMax(margins) and Dodgson:

It is well established and well-discussed on EM that MinMax(margins)
has particularly great problem with strategic truncation and offensive

Those things, even offensive burial, aren't a problem with SITC,
because the only candidate who can benefit from it is the most
top-ranked candidate among the unbeaten candidates--or just the most
top-ranked candidate if there are no unbeaten candidates.

Offensive burial can't make anyone else win.

I'll try to answer (only) the parts of this posting that I didn't
answer in part 1 of my reply:

> I don't think the following four questions that you gave as a response are ones that I left unanswered, but new questions or new formulations. I'l check them anyway.
>> 1. What makes you think that MinMax(margins), Dodgson, or Beatpath
>> won't have a chicken dilemma?
> I already said that I do believe that basic Condorcet methods are not very prone to this problem. I >know that you disagree. Maybe you'll find one day a proof that will convince me.

Above, in this reply, I've posted an example in which defection by the
B voters is rewarded. The A voters, expecting likely defection by the
B voters can co-operate, by ranking B, because at least one faction
must co-operate in order to defeat C. But, if they do, they'll lose to
B, because they've been had by the B voters.

That's the chicken dilemma, and it's fully there, with MinMax(margins)
and Dodgson.

As for Beatpath, Beatpath's failure was shown in my posting with my
old 27,24,49 example. It's easier to show Beatpath failing, having the
chicken dilemma. But, as you can see from the example shown above in
this post, MinMax(margins) and Dodgson fail quite easily too.

>> Must I do that, to show you their
>> chicken dilemma? Request it and I will.
(I showed an example, in this posting, in which MinMax(margins) has
that problem.

> No need since I don't expect that to change my opinions. It could be a wasted effort. I'm >interested if there is something really convincing, but maybe better leave this topic this time, with >the assumption that I would not believe it anyway.

If an example of it happening doesn't convince Juho, then nothing
will. That's ok.

You said:

Many Condorcet strategies are difficult to identify, to use, to
coordinate, and often they may also backfire.


Sure. As I said, in Condorcet, even in a u/a election, you won't know
what to do. For example, in a u/a election:

Approval: Approve the acceptables and none of the unacceptables.

Score: Top rate the acceptables and bottom rate the unacceptables.

SITC: Top rank the acceptables, and don't rank anyone else.

Unimproved Condorcet (Including MinMax(margins), Dodgson, Beatpath,
etc.): You still have the same need to top rank the acceptables, and
for the same reason. But, with Unimproved Condorcet,
that can, as you said, backfire, because top ranking someone (you
don't know which one) could cause your last choice to win. In
Unimproved Condorcet, you won't know what to do, even in a u/a

But suppose there is one Democrat, and some Republicans. There are
also some progressives whom you prefer to the Democrat. You believe
(you've always heard it in the media, which you completely believe)
that the Democrat and the Republicans are the only candidates who can
win. You feel that the Republican is unacceptable, and that the
Democrat is acceptable, and that it is all-important to ensure that
the Republican doesn't win.

What do you do? Your optimum strategy is to rank the Democrat _alone_
in 1st place. Now, if there are several Democrats, then you have a
problem. You then have a dilemma that you wouldn't have in Approval,
Score, or SITC. You must try to guess which Democrat(s) to top rank,
but you know that one of them (you don't know which) could, by being
top-ranked, change the win from a Democrat to a Republican.  That's a
dilemma that you wouldn't have in Approval, Score, or SITC.

>The details have been debated in the EM list.

But the specifics of the above-described situation haven't been
discussed. u/a elections have been little discussed here, other than
by me. Of course yes, unimproved Condorcet's FBC failure is well known
and well-discussed at EM.

>> Sometimes you seem to say that you're just speaking in general, about
>> most societies, or many societies. Sometimes, though, you make
>> assertions about what won't happen here.
> I started with general claims but I commented also the U.S. related stuff since that seems to be >on your agenda.

That's right, you did. You sometimes do, but then, at other times, you
insist that you're only speaking generally, about most societies, or
about a matter of "maybe".

>> 3. What is your best argument to support your belief that Dodgson,
>> MinMax(margins) or Beatpath would do better at choosing the ideal
>> sincere winner, if voting were sincere, than SITC would do?
> I don't claim that. I left the selection of the sincere winner criterion open.

Of course that means that you can't use it. You can only speculate. Of
course that's what you've been doing.

You said:

As already noted, methods that are strongly strategy defence related
may not be exactly built to reflect targets that have been set for
selecting the winner based on sincere votes.


You're repeating, again, something that I've answered--the first time
you said it, and also in each repetition.

Choosing well under sincere voting, and not causing favorite-burial
incentive aren't mutually incompatible, because they both result from
respecting the voters' preferences, intent and wishes.

Aside from that, I don't know if you're aware that you're talking pure
speculation, about how (you believe) maybe there could be a problem,
unspecified by you.

>> 4. Tell the requirements that describe the ideal sincere winner.
> I repeat, I left the selection of the sincere winner criterion flexible and open.

Thereby, you left yourself with only some pure speculation.

> I presented one >example definition that could be used somewhere.

I answered about Dodgson and MinMax(margins).

> If you want some more generic comments, I might say that a good ideal sincere winner definition >is supposed to tell what kind of properties the society wants the winner to have. It does not care >about strategic vulnerabilities and does not defend against them.

Is that right. Funny, but this society's mass media regularly claim
that favorite-burial strategy is needed "So that you won't waste your
vote, you must vote pragmatically." Nearly all of the voters obey
those instructions.

Oh, but that's right: You were only referring to most societies, or
many societies.

I guess you're talking about how a society _should_ be. This "ideal
single-winner definition"--where would it be useful? La La Land?

You said "supposed to". Supposed by whom? You?

You're vaguely referring to some supposed ideal or standard, without
saying whose ideal or standard you think it is.

You said:

You could want the winner to be a person that is accepted by all,
supported by majority, one that has strong support of some major
party, one that has wide geographical support, support in all age
groups, one that is not hated by any state, or whatever that makes the
winner good. Once you know what you want, you can pick a practical
election method that elects such a candidate (or is close enough),
maybe tries to defend against strategies, is simple enough to use etc.


Or you could just seek to carry out what the voters themselves choose,
instead of your antidemocratic, autocratic Soviet-like
social-engineering goals.

While you're at it, it would be nice if the voting system doesn't
discourage sincere voting, at least not to an easily-avoidable
reasonable degree (No favorite-burial incentive. If it's a rank
method, no chicken dilemma).

>> Certainly SITC is a different method from Dodgson or MinMax(margins).
>> It wasn't clear that that's what you meant. But, if that's what you
>> meant, then you're right about that.
>> So what?
> That was part of my basic claim that best winner criteria and methods that aim at being strategy >proof are different.

Your completely unsupported claim about that.

You said:

You seem to be close to saying that SITC is not only a relatively
strategy resistant method but also (close to) your definition of an
ideal winner with sincere votes.


I said that the CW is a widely-accepted notion of the ideal sincere
winner. But change that to legitimately-defined CW.

But the more your voting system forces drastic departure from sincere
voting, the less sincere voting you're going to get.

>> You mean the status against opposition in office of the candidate
>> whose largest margin against him, in favor of another candidate, is
>> the least. And being the most favorite, having the largest faction,
>> doesn't confer any status against opposition in office? :-)
> Yes, the "least additional support/votes required" criterion (as a definition of good sincere winner) >points in that direction.

You're telling us your own personal opinion about what would (maybe)
be the ideal sincere winner (in the event of a circular tie).

You keep saying it, but that isn't the same as supporting it.

I'm not going to keep on repeating my answers to that. I refer you to
my previous replies, where I've answered that statement of yours many
times--each time, in various ways.

You said:

I don't know what "most favorite" and "largest faction" exactly mean


That's funny, because I just finished defining them, in the post to
which you're replying.

"Most favorite" was a brief wording for "Voted in 1st place by the
most people". First place is the most favored place. So I was
referring to the candidate most favored with 1st place ranking.

The "largest faction"?  Maybe I'd better define two words for you:
"Faction" and "Largest".

A "faction" refers to a set of people (voters in these discussions)
who share some preferences or wishes, and co-operate toward achieving
what they want. In voting system discussion, we're referring to a
faction of voters who have sufficient preferences or goals in common
that they support and vote for the same candidate as favorite, or at
least for many of the same set of candidates.

In particular, in the examples that I've been posting, I made it clear
that the A faction prefers candidate A as 1st choice, and that the B
faction prefers candidate B as 1st choice, and that the C faction
prefers candidate C as 1st choice. That defines the factions, in that
usage. Factions defined by whom they most want to elect.

"Large". The large-ness of a faction refers to the number of voters in
that faction. No, contrary to what you thought, it has nothing to do
with the body-size of the individual persons.

The "-est" in "Largest": That means "more large than the others."

Let me know if you still don't understand what a faction is, or what
"largest faction" means.

At least I should give you credit for making a statement that isn't a
repetition. But you should have checked a dictionary.

About the repetition: I'm not going to keep on answering statements
that you keep repeating. I've done that enough. More than enough.

>1, but I think they are not addressed by the "least additional support/votes required" criterion.

...required to make the candidate CW.

That isn't a criterion. It's the definition of Dodgson.

You may personally like Dodgson (though like to mistakenly call it
"MinMax(margins)), but merely stating its definition doesn't establish
it as the standard by which to evaluate method when there's a natural
circular tie under sincere voting. You're only expressing an opinion.

You're welcome to your opinion. You haven't told why anyone else should agree.

Why should the candidate who could most easily be made into CW by
adding (or subtracting, or disregarding, or reversing) the fewest
pairwise votes be the ideal sincere winner in a natural circular tie?
Because you think so? That isn't enough.

When you rank someone in 1st place, or when you rank a set of
candidates in 1st place, it's because you want to help them win
instead of the ones you didn't rank in 1st place. The candidate who
has been so voted by the most people has strong claim to be the
rightful winner when there is no one unbeaten, or no one uniquely

No, I'm not advocating Plurality--largely because of its strategy
problems. But as a Condorcet completion, the favoriteness standard (a
short name for what I described in the paragraph before this one)
doesn't bring Plurality's problems, and has a valid claim to
rightness. Certainly such a candidate, after being elected, has
undeniable strong authority against opposition in office

But I've said that before too. I'll repeat that I'm not going to keep
repeating the answers to your repeated remarks.

You said:

It is characteristic to Condorcet methods (like Minmax(margins)) that
they can sometimes elect compromise candidates that have limited first
preference support.


Don't worry about that. That's for the voters to choose, for
themselves. If you don't like a compromise, then I advise you not to
support him, even as a compromise. You don't like the alternative?
Well, you do have a problem, don't you. But don't blame it on the
voting system.

There are a number of justifications for electing CWs. They tend to
have good social utility. They're the candidate who would be elected
in repeated elections, eventually arrived at, when everyone find out
eachother's preferences. They're, therefore, the natural strategic
choice. Oops, there's that word that you don't like.

I only advocate SITC for informational polling. I don't recommend
anything other than Approval and Score for official public elections.

But, if we had to have a rank method, SITC would be the best choice.
If you want to propose some rank method, for any purpose, then I
suggest that SITC would be better. I've amply told why.

Mike Ossipoff

More information about the Election-Methods mailing list