[EM] Re: SCRRIRVE & MO's example

[Chris Benham]

On  Wed. Jan.21,2004  I  posted:

Here is an example that Mike Ossipoff posted (Tues.Jan.20)
Presumed sincere preferences:
40:A>B>C
25:B>A>C
35:C>B>A
100 ballots. B is the Condorcet Winner (and the SCRRIRVE winner).

A voters Bury (offensively order-reverse against)B, while all other 
voters vote sincerely:
40:A>C>B
25:B>A>C
35:C>B>A
All candidates in the Schwartz set. B>A>C>B.
RP, Beatpath, Simpson, Raynaud all elect A.
SCRRIRVE eliminates A and elects C, so the A voters' strategy back-fires.

A voters Bury B, and B voters (maybe in response) truncate:
40:A>C>B
25:B
35:C>B>A
As in the last example, B>A>C>B.

Discussing Raynaud, Mike writes:
"B has the biggest pairwise defeat, 75. B is eliminated, and with just A 
& C remaining, A is now the unbeaten candidate and wins.

With wv, the A voters' offensive order-reversal backfires, due to the 
defensive truncation, and is therefore well-deterred."

Wv elects C, as does SCRRIRVE.

Mike's reply (Fri.Jan.23) included this comment on terminology:

"Let me just point out that the term "offensive order-reversal" was in use 
for years before Blake renamed it "burying". Brevity is convenient, but the 
trouble with "burying" is that sometimes one can  bury defensively, 
sometimes offensively, and "burying" doesn't distinguish those, except for 
the reason that Blake probably defines 'burying' as offensive 
order-reversal.  For instance defensive burying is needed in Plurality,IRV and 
Margins. I'm not objecting to "burying", since it's briefer, but I just 
wanted to point out which term was in use first, and the meaning fault that 
"burying" has." (with small "typos" corrected)

I understand that the Cretney/Schulze definition of "Burying" is to "(insincerely) down-rank a
candidate to try to make that candidate lose". Normally the Buriers are trying to elect their
favourite,so they vote their sincere favourite in first place. 
The other order-reversal strategy is called "Compromising", which means to "up-rank a candidate
to try to make that candidate win." Normally the Compromisers are "betraying" their favourite and
voting their "compromise" in first place.
Of course it is possible for a voter to do both at once (especially in say Borda), and that is not
a problem.

MO:"I guess Chris didn't get what I said the other day: All you've proven with 
the example is that uncountered offensive order-reversal can succeed in wv 
(whether the method is MAM, BeatpathWinner, or any other wv version)."

You forgot to add "in a situation where it fails in SCRRIRVE".

MO:"But no one here has denied that offensive order-reversal can succeed in wv.
In fact, offensive order-reversal can succeed in every method that doesn't 
have a worse problem.(For instance, IRV & Plurality have worse problems)."

I don't (and didn't) deny this.

MO:"The example, as I explained before, doesn't show that SCCIRVE doesn't ever 
let offensive order-reversal succeed."

I didn't say it did.

MO:"Will Chris demonstrate that offensive order-reversal can't succeed in 
SCRRIRVE?"

That would be difficult, because in the post in which I introduced (CC)SCRRIRVE,I quoted an
example from a James Green-Armytage post in which "uncountered" Burying succeeds in CCSCRIRVE
(as it does in wv.) The difference there was that "defensive" truncation by the supporters of
the sincere CW was sufficient to elect that CW in SCRRIRVE, but not in wv.
That James G-A post:
http://lists.electorama.com/pipermail/election-methods-electorama.com/2003-August/010653.html
My initial (CC)SCRRIRVE post: 
http://lists.electorama.com/pipermail/election-methods-electorama.com/2004-January/011679.html

Here is Adam Tarr's "signature example on this list":

Presumed sincere is:
49: R>C>L
12: C>R>L
12: C>L>R
27: L>C>R

100 ballots. C is the CW (and the SCRRIRVE winner).

R voters truncate:
49: R
12: C>R>L
12: C>L>R
27: L>C>R

L>C>R>L.  L is eliminated and  C wins (as in wv).

R voters bury C:
49: R>L>C
12: C>R>L
12: C>L>R
27: L>C>R

R>L>C>R.   The Burying strategy backfires,  R is eliminated and  L wins.
RP, Beatpath, Simpson etc. all elect R.

I have shown several examples where (CC)SCRRIRVE performs BETTER than wv at resisting Burying,
and I have not been able to find ANY in which it performs worse. If one could be found, you'd
think that a veteran prolific-poster wv advocate would be kind enough to post it.

Chris Benham








 


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