[EM] Re: optimal Condorcet truncation

[Russ Paielli]

Chris Benham chrisbenham-at-bigpond.com |EMlist| wrote:
> 
> Russ,
> You wrote (Sat.Feb.26):
> "A more useful criterion is the normal (as opposed to Mike-style)
> criterion taken from Blake Cretney's website:
> 
> Name: Secret Preferences Criterion: SPC
> Application: Ranked ballots
> Definition:
> If alternative X wins, and some of the ballots are modified in their
> rankings below X, X must still win.
> 
> Condorcet does not pass this criterion, which tells us that voters have
> incentive to truncate in some cases if not routinely."
> 
> Woodall splits this somewhat oddly-named criterion into two fairly 
> self-explanatory others:
> 
> "Later-no-Harm: adding a later preference to a ballot should not harm 
> any candidate already listed", and
> "Later-no-Help: adding a later preference to a ballot should not help 
> any candidate already listed".
> 
> Condorcet passes neither of these, but your conclusion  only applies to 
> Later-no-Harm.
> In WV Condorcet (BP/RP/MM/River), the two LNHs are not in balance 
> (adding a later preference is more likely
> to help than harm an already listed candidate)  so that in the 

Interesting. Your telling me that adding a preference is more likely to 
help than harm a higher-ranked candidate? That's non-intuitive if it's 
true. I can certainly see how adding a preference might help a 
particular higher-ranked candidate in certain circumstances, but I don't 
see how it could help on average for all the higher-ranked candidates. 
If it does, than I'd call that a fault of the election method. Can you 
prove that or point me to a proof?

> zero-information case there is a random-fill incentive.
> 
> As Kevin Venzke just more-or-less pointed out, the right 
> zero-information strategy in WV is to equal-rank the candidates
> above some ("the") approval cutoff point and to strictly rank 
> (random-filling if necessary) all the candidates below it.

And what if equal rankings are not allowed?

--Russ