[EM] Jobst: Strategy-Free Criterion
nkklrp at hotmail.com
Tue Sep 13 17:15:11 PDT 2005
Sorry to break my retirement promise again, but this time it will just be
temporary. At almost the exact same time that I retired from voting
systems, a Range-Voting advocacy organization was formed, and I couldn't
resist taking part to some small extent. In for a dime, in for a dollar. For
me, either I'm completely out of something, or I'm not out of it at all. So,
I made a short postponement of my retirement.
So I was browsing the EM archives, and I noticed a message posted in March,
which I'd missed at the time. So I'm going to reply to it now:
>Here´s the actual definition of SFC:
>If no one falsifies a preference, and if a majority prefer the CW to
>candidate Y, and vote sincerely, then Y shouldn´t win.
>[end of SFC definition]
>Which part of that don´t you undestand?
You (Jobst) replied:
Well, I at least think I understand it, assuming you speak of the
*sincere* CW (otherwise, that is, if you meant CW according to the cast
prefernces, then each Condorcet method would fulfil SFC trivially by
definition, and that cannot be what you meant).
1. I was writing that to someone else. You weren't then a participant in
that discussion,and I was not questioning your understanding of SFC.
2. The "sincere" CW is the only kind that I've heard of. Though some people
have, at times, misused the term by applying it to the BeatsAll candidate,
the definition of a CW is pretty much agreed-upon by all. Though the
definition is worded in different ways, some more precise than others, this
is what it always means:
A Condocet winner is a candidate who, when compared separately to each one
of the other candidates, is preferred to that candidate by a number of
voters greater than the number of voters who prefer that candidate to
[end of CW definition]
Maybe the wording could be made clearer by naming the candidates:
A Condorcet winner, is a candidate, C, who, when compared separately to
each other candidate, X, is preferred to X by a number of voters greater
than the number of voters who prefer X to C.
[end of alternative wording of CW definition]
Often an author will just say that the CW is a candidate who'd beat each
other candidate in separate 2-candidate races. That means the same thing,
though it isn't really as complete.
Anyway, that definition, worded in these several ways, and maybe a few
others, is the only accepted definition of a CW. So the "sinceree" CW is the
But: Can you tell me just one method which passes that criterion?
No. But I can tell you a class of methods that pass that criterion: All of
the wv Condorcet versions pass SFC.
These include the wv versions of BeatpathWinner, CSSD, SSD, Ranked Pairs,
MAM, PC, Smith//PC, and SD.
Additionally, one of the recently-described FBC-complying rank methods
Approval certainly doesn't.
Correct: Approval doesn't pass SFC. But Approval passes FBC, which
Condorcet-Criterion methods don't pass, and which is absolutely necessary
for today's public political electorates, for whom there's a "greater-evil"
whose defeat is so important that people feel a need to abandon their
favorite, if necessary, in order to beat him.
Approval additionally passes WDSC, which not many methods pass. Approval
also has a valuable optimization property described at the CRV website.
Range-Voting (also called CR, or the point system) likewise passes FBC and
WDSC, and shares that optimization property.
So, although I find anti-strategy criteria most important and are
completely d'accord with you that their formulation will of course
contain references to the sincere preferences of the voters, I still
don't think that this particular criterion, at least not in the above
version, is particularly useful...
You seem to be saying that you don't find SFC useful because Approval
doesn't pass SFC. But then you must not find Condorcet's Criterion or the
Smith Criterion useful either.
Or is it that you're assuming that no method meets SFC? But I've said many
times on EM, and at the websites that have my articles, that the wv
Condorcet versions all pass SFC.
SFC is a majority-personalized version of Condorcet's Criterion (CC). CC
makes a guarantee to the entire electorate, that if they vote sincerely the
CW will win. But maybe we can't guarantee that everyone will vote sincerely.
So SFC makes a guarantee to a majority who prefer the CW to some candidate
Y, stipulating that they, but not necessarily anyone else, vote sincerely. A
particular prefernce-group can more reasonably assume that they vote
sincerely, as opposed to assuming that everyone, including the voters they
disagree with most, will vote sincerely. SFC is majority-personallized CC.
That's why I prefer SFC to CC, and considcr SFC more "useful" than CC.
Because maybe not everyone will vote sincerely.
There are several voter-set-sizes to which a criterion can make its
guarantee. Obviously the best is for a criterion to make a guarantee
individually to each and every voter. For instance, FBC guarantees, to each
voter individually, that s/he has no reason to vote someone over his/her
But I wanted to guarantee more, and the additional guarantees that I wanted
to make can't be made to each individual. But they could be made to a
majority. Hence the majority defensive strategy criteria, of which SFC is
Condorcet's Criterion is an example of a criterion makes its guarantee to
the largest voter-set, the entire electorate, while stipulating sincere
voting by all.
The more people whose sincerity has to be stipulated, the less useful the
criterion is, obviously.
FBC is essential for public election methods. But in organizations and
committees of honest people who aren't too antagonistic to eachother, where
there's no really scary "greater-evil", FBC isn't so necessary. The wv
methods can fail FBC, but not easily. Without a scary greater-evil, we
needn't worry about wv's FBC failure so much. Under those conditions, wv's
SFC compliance becomes very valuable. To a lesser, but still meaningful,
extent, its CC compliance becomes useful too. That's why I've been
recommending BeatpathWinner/CSSD to organizations and committees for a long
Of course if an organization wants to use, for its own elections or choices,
a more publicly winnable method, in order to demonstrate the method or help
set a use-precedent for it ,then RV would be the best choice.
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