[EM] Chris SFC reply

[Michael Ossipoff]

Thank you, Chris, for posting this quote from my web definitions:
Pasting from Mike's page:
Some definitions useful in subsequent criteria definitions:
A voter votes X over Y if he votes in a way such that if we count only his 
ballot, with all the candidates but X & Y deleted from it, X wins.
[end of definition]
Voting a preference for X over Y means voting X over Y. If a voter prefers X 
to Y, and votes X over Y, then he's voting a sincere preference. If he 
prefers X to Y and votes Y over X, he's falsifying a preference.
A voter votes sincerely if he doesn't falsify a preference, and doesn't fail 
to vote a sincere preference that the balloting rules in use would have 
allowed him to vote in addition to the preferences that he actually did 
vote.
[end of definition]
Strategy-Free Criterion (SFC):
Preliminary definition: A "Condorcet winner" (CW) is a candidate who, when 
compared separately to each one of the other candidates, is preferred to 
that other candidate by more voters than vice-versa. Note that this is about 
sincere preference, which may sometimes be different than actual voting.
SFC:
If no one falsifies a preference, and there's a CW, and a majority of all 
the voters prefer the CW to candidate Y, and vote sincerely, then Y 
shouldn't win.
[end of definition]


Chris quotes me:

Michael Ossipoff wrote:
Kevin and Chris posted their criteria that they incorrectly claimed 
equivalent to SFC.

These same alternative "SFCs" have been posted to EM before and thoroughly 
discussed before.
In fact, we've been all over this subject before.

Chris replies:

So why don't you point us to where in the EM archive we can find this 
earlier discussion?


I reply now:

I’d be glad to, if I knew the exact, or even approximate dates of the 
discussion. Is the archive searchable? It was only a few years ago.



Chris continues:

Are they in your opinion equivalent for
ranked-ballot methods?

I reply now:

They may well be. But I like criteria that apply seamlessly to all methods.

Chris quoted me:

Though Chris's and Kevin's criteria clearly are not equivalent to SFC, maybe 
someone could write a votes-only cirterion that is. First of all, what's 
this obsession about "votes-only"?

Some people worry that criteria that give the appearance that we have to 
read voters' minds to see if they are met are not the easiest to check for.

I reply now:

Appearances can be deceptive. Your worry is needless. No one has to read 
anyone’s mind to apply my criteria. Look at the claimed failure example. 
Look at the criterion to find out if the claimed failure example meets the 
premise conditions of the criterion. Then look at the claimed failure 
example to find out if its outcome fails to meet the criterion’s 
requirement. You don’t have to read any minds, because the claimed 
failure-example can specify whatever preferences the example-writer wants to 
specify. Are they consistent with those stipulated in the criterion’s 
premise?

As I said, it doesn’t even matter what “prefer” means. Just compare the 
preferences specified in the claimed failure example to those stipulated in 
the criterion’s premise. Are they consistent? How difficult is that? As I 
said, if it makes you happier, you could substitute “outgribe”, or any other 
Lewis Carroll nonsense verb, or any other meaningless word, for “prefer”.

As I also, said, I’ve posted a precise, abstract definition of “prefer”. I 
couldn’t tell you exactly what date it has in the archives, right now, but I 
could find it.

But, as I said, it doesn’t matter if “prefer” means anything.

Chris quoted me:

Now, quite aside from that, the efforts to write a votes-only equivalent 
criterion seem motivated by a desire to not say things that happen to be 
what I want to say. I want SFC to be about the fact that that majority, 
because they all prefer the CW to Y, and because there’s no falsification 
(on a scale sufficient to change the outcome), can defeat Y by doing nothing 
other than voting sincerely.

To say it in a way that doesn’t say that wouldn’t be SFC. If someone wrote 
such a criterion, then I’d recognize it as a _test_ for SFC compliance, but 
not as SFC. When I say that a method passes or fails SFC, and someone says 
“What’s that?”, then I want to tell them the SFC described in the paragraph 
before this one, the one that relates to the CW, no need for other than 
sincere voting by the majority and non-falsified voting by everyone else. If 
I worded it like Kevin or Chris, it wouldn’t be self-evident why it’s 
desirable to meet that criterion.

Someone could suggest that I use an alternative as the criterion, and save 
my SFC as a justification. No, I want the criterion’s value to be 
self-evident.

Chris replies:

Well its value as something distinct from the Condorcet criterion isn't 
self-evident to me. If this CW>Y majority can't elect the CW, why do they 
necessarily
care if Y is elected or not?

I reply now:

I doubt that it would bother you if someone won whom you like more than the 
CW.

Chris continues:

And the way you've dressed this up, I can't see how it really qualifies as a 
"strategy criterion".

I reply now:

It’s a strategy criterion because it’s about voters’ need for strategy. It 
describes plausible conditions under which the voters referred to don’ t 
need any strategy. Should we call it, instead, a “no-strategy criterion”?

Chris continues:

How are the members of this CW>Y majority supposed to
know whether or not anyone "falsifies a preference"?

I reply now:

Wouldn’t it be nice if voters had complete information about things like 
that. I’m sorry, but I can’t give you that. But I can assure you that 
falsification, on a scale sufficient to change the outcome, will be 
difficult to organize, and will be rare.


Kevin continues:

And if they do know what are they supposed to do about it?

I reply now:

That’s beyond the scope of the criterion. It’s about a guarantee that they 
have if falsification _doesn’t_ occur (in practice it need only not occur on 
a scale sufficient to change the outcome).

But if you think people are going to do offensive order-reversal, then don’t 
rank any lower than where you guess the CW is. Or, as I would do, don’t rank 
a candidate of voters likely to order-reverse. Which is probably the same as 
saying don’t rank any disgusting candidates. Which is really a good policy 
anyway.

Chris quotes Eppley:

From Steve Eppley's MAM page:

truncation resistance: Define the "sincere top set" as the smallest subset
of alternatives such that, for each alternative in the subset, say x, and
each alternative outside the subset, say y, the number of voters who
sincerely prefer x over y exceeds the number who sincerely prefer y
over x. If no voter votes the reverse of any sincere preference regarding
any pair of alternatives, and more than half of the voters rank some x in
the sincere top set over some y outside the sincere top set, then y must
not be elected. (This is a strengthening of a criterion having the same name
promoted by Mike Ossipoff, whose weaker version applies only when
the sincere top set contains only one alternative, a Condorcet winner.)

Chris says:

This makes some sense as a strategy criterion, being about deterring a 
faction from truncating against the members of the sincere
Smith set. The "weaker version" ascribed to you seems easier to test for.

How does that version differ from your present SFC?

I reply:

Steve’s criterion is based on GSFC, the generalization of SFC to the Smith 
set. But it’s different from GSFC in a number of ways:

1. It requires only that no one order-reverse. GSFC & SFC require that no 
one falsify. An indifferent voter who votes a preference falsifies but 
doesn’t order-reverse. Steve’s criterion won’t work unless he changes 
“reverse” to “falsify”.

2. Steve’s criterion is written to apply only to rank methods. Or if you 
interpret it to apply to all methods, it’s met by Plurality.

Oddly, though not wanting to mention the preferences of that majority, Steve 
doesn’t mind mentioning preference when defining the sincere Smith set 
(sincere top cycle).

Steve mistakenly calls it a strengthening of SFC, as if it were GSFC.
Steve’s criterion is not GSFC.

Mike Ossipoff


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