Truncation Resistance #2 criterion (was Re: First Choic

[Steve Eppley]

Hugh T wrote:
>Steve's proposed consensus censorship 

Censorship seems too negative a description, since I provided the
reasonable "escape clause": someone proposing a new method which
fails TR-2 needs only include some other criterion--maybe I should
have said "standard"-- satisfied by his/her proposed method better
than Condorcet or Smith//Condorcet, and explain why that criterion
matters.

There may be some value to the list in having people propose methods
which are inferior on some standards and not superior on any.  It 
could stimulate invention of better methods, or help us understand
why known methods are better than the proposals.  But I'd like the 
authors of those proposals to be clearer about what they're writing;
if they think the proposal may be better on some standard, we deserve
to know which, and if they don't, we deserve to know that too.

If Hugh wants this list to welcome proposed methods which are offered
up without explaining why they may be better, and they routinely turn
out to be badly flawed, I'd appreciate it if he would better share
the burden of analyzing their faults.  Freedom of speech works best
when there are a lot of people willing to point out the bugs in
"bad" speech.

>raises the questions: (1) Why is truncation resistance more
>important that resistance to order-reversal?
-snip-

Because truncation will probably be a common occurence when there
are many candidates, even with "sincere" nonstrategically-minded
voters.

>(2) Why it it critical to prevent a putatively organized and devious
>group of plurality voters from achieving through truncation what
>they could also achieve by insincerely dividing their second choices
-snip-

Can we agree to make the following assumption? 

    The level of "strategic sophistication" will be fairly even 
    among all the groups. 

Truncation will occur even with low deviousness (and maybe
especially with low deviousness), but massive reversal requires a
highly devious group.  If the assumption above is correct, the
reversal will be easily countered by one of the other similarly 
sophisticated groups.

>I submit that a system which reaches a different result from
>Steve's second example if the "A" voters are divided into 23AB and
>23AC creates a clear incentive to insincere voting.
-snip-

The "largest loss" scores in Hugh's example are very close:   
    A=54, B=57, C=56
A wins if the B and C voters roll over and play dead.  But the
numbers are so close that a small defense is sufficient to counter 
the massive reversal.  And they're so close that the counter may
make the reversal backfire by electing C. 

Is it plausible the A voters will be able to successfully reverse
without the B and/or C voters easily defending?  TR-2 guards against
both innocent and devious truncation.  The other voters (a majority)
can guard against, and maybe punish, devious reversal, just by making
sure that B and/or C aren't both beaten by a majority. 

---Steve     (Steve Eppley    seppley at alumni.caltech.edu)