[EM] Rank methods for public proposal

[Michael Ossipoff]

On Feb 20, 2007, at 15:39 , Michael Ossipoff wrote: > Juho wrote: > > My 
sympathies towards minmax(margins) come primarily from the way > it handles 
sincere votes. > > I reply: > > But there won’t be sincere votes for it to 
handle, to the extent > that it doesn’t allow sincere votes. That’s why the 
defensive > strategy criteria, and the wv Condorcet methods were proposed.

Juho replies:

Do you mean that margins would be so "strategy inviting" that most voters 
would turn to strategic voters (in practical real-life elections) if margins 
are used?

I reply:

Yes, voters would be more likely to regret sincere ranking in margins than 
in wv.

Juho continues:

And that WV would solve that?

I reply:

Yes. By meeting SFC. And by making it much easier to deter offensive 
order-reversal, merely by not ranking the perpetrators’ candidate.

Juho continues:

(I'm under the impression that this kind of impacts are not very big and 
that they may work in both directions.)

I reply:

WV is much more strategy-free. The difference is unidirectional.

Juho continues:

I think Dodgson counts the sum of defeats. I'm not talking about that, just 
basic minmax(margins) (that actually implements "additional votes needed to 
become the Condorcet winner").

I reply:

But Minmax only scores the candidate according to his worst defeat. That 
doesn’t tell what it would take to get rid of all of his defeats and make 
him the CW. Dodgson does that. But Dodgson fails Clone Independence and all 
of the defensive strategy criteria.


Minmax is used with more than one meaning, and so it’s best to call PC by 
the name PC.



I’d said:

 > “Minmax isn’t a good method name, because it’s used with more than > one 
meaning.

Juho replies:

Also with other meanings than minmax(margins), minmax(winning votes) etc?

I reply:

Yes, it’s often used to refer to Simpson-Kramer, a method defined in the 
Winter ‘95 Journal of Economic Perspective in a way quite different from PC.

Juho continues:

>The defensive strategy criteria and wv Condorcet were proposed for > a 
>reason. ... As I already mentioned I don't like counter strategies to much.

I reply:

Then you’d like methods that meet SFC, because they’re much more free from 
need for counterstrategies. The wv Condorcet methols meet SFC. Additionally, 
SFC is met by MDDA.  Also, MMPO meets SFC, but was shown to have some kind 
of a problem that could cause serious embarrassment.

I’ve proposed MDDB, which also meets SFC. MDDB replaces the approval count 
with an SR count, for part two, to choose among the un-disqualified 
candidates.

SR (Summed Ranks): Elect the candidate over whom (summed over all the 
ballots) fewest candidates are ranked.

[end of SR definition]

MDDA & MDDB also meet FBC, as does SR. MDDA meets SDSC, but MDDB probably 
fails that and WDSC.  But MDDB could have a better chance of acceptance than 
MDDA, if MDDA is rejected because of anti-Approval prejudice.

SR, meeting only FBC, is a substitute for Approval, if, as seems to be the 
case, Approval can’t get accepted by the public.

I’d propose SR only if the better rank methods couldn’t gain acceptance, and 
if SR’s simplicity made it the only accepted rank method. And, of course, 
only if Approval can’t get accepted, which, from my conversations with 
members of the public, seems to be the case.

Anyway, a number of methods meet SFC: wv Condorcet, MDDA, MDDB, and MMPO.

Juho continues:

If real-life elections end up in media and parties proposing various counter 
strategies to voters one day before the election (to strategies that some 
groups are planning or might try) I'm sure that election method would 
receive some criticism.

I reply:

Yes, but of course that’s exactly what always happens with Plurality.

The best methods won’t have that problem.

Juho continues:

I'm more interested in methods where strategic voting stays at levels where 
no counter strategies need to be considered (and where strategies are not a 
serious risk in the first place). > The wv Condorcet versions are much more 
free of strategy-need, and > much more resistant to offensive strategies 
(for instance, > offensive truncation isn’t a problem in wv Condorcet). 
There are also examples in the other direction. - Sincere votes: 49:A, 
49:BC, 1:CB => B wins - Strategic votes: 49:A, 49:BC, 1:CA => C wins if 
winning votes are used

I reply:

It’s never been denied that offensive order-reversal can be a problem in 
Condorcet. It’s much more of a problem in margins than in wv. One of the 
advantages of wv over margins is that, in wv, offensive order-reversal is 
easily thwarted by simply not ranking the reversers’ candidate. In other 
words, in wv, you can succeed with offensive order-reversal only if your 
victims are trying to help you. Would that make you feel proud of yourself? 
<smiley>

So, if you don’t want a problem with offensive order-reversal, I recommend 
wv to you.

Juho continues:

I however hope that we are discussing rather small differences in strategic 
performance here

I reply:

No.

Juho continues:


(since my basic thinking is that Condorcet methods are at their best in 
situations where strategic voting will not become a major issue due to the 
natural strategy resistance of all Condorcet methods).

I reply:

You mean, due to the natural strategy resistance of wv Condorcet methods.


Juho continues:

Yes, good criteria are exact. But too often I see argumentation that refers 
to scenarios that are possible in theory but that maybe never occur in 
practice and/or whose impact is minor and/or requires lots coordination, 
many strategic voters, has risk of failure etc

I reply:

Good point. Offensive order-reversal, the only thing that could cause a 
strategy problem in wv (truncation causes a strategy problem in margins), 
requires lots of co-ordination, many strategic voters and has great risk of 
failure--especially in wv, where it’s so easily thwarted, merely by not 
ranking the perpetrators’ candidate.

In margins, a CW could be defeated by truncation even if it is inadvertent, 
lazy, hurried, or otherwise non-strategic. But of course the election could 
be stolen from the CW by strategically-intended truncation too, in margins.

Mike Ossipoff



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