[EM] Condorcet/Range DSV

[Jameson Quinn]

> This Condorcet-Range hybrid you suggest seems to me to inherit a couple of
> the problems with Range Voting.
>

Fair enough.


>
> It fails the Minimal Defense criterion.
>
> 49: A100,  B0,  C0
> 24: B100,  A0,  C0
> 27: C100,  B80, A0
>
> More than half the voters vote A not above equal-bottom and below B, and
> yet
> A wins.
>

True. Yet B could win if the C voters rated B 99, which would still be
Condorcet-honest.


>
> Also I don't like the fact that the result can be affected just by varying
> the resolution
> of  ratings ballots used, an arbitrary feature.
> I think it would be better if the method derived approval from the ballots,
> approving all
> candidates the voter rates above the voter's average rating of  the Smith
> set members.
>

That is not a bad suggestion; I like both systems. Yours gives less of a
motivation for honest rating: In most cases, it makes A100 B99 C0 equivalent
to A100 B51 C0. I guess you'd give exactly half an approval if B were at
exactly 50?

Anyway, the main motivations for a DSV-type proposal like this is to make it
really rare for voters to have enough information to strategize without it
backfiring. I think that including full range information (that is, my
proposal as opposed to yours) makes the voter's analysis harder, and so
makes the system  more resistant to strategy. Under honest range votes, it
also helps improve the utility.


>
>
> "For strategies which don't change the content
> of the Smith set, it does very well on other criteria, fulfilling
> Participation, Consistency, and "Local IIA". "
>

Sorry, I wasn't clear. If the content of the smith set DOES change, this
method fails all those criteria. See below for argument of why that's not
too bad.


>
> "And because it uses Range ballots as an input but encourages
> more honest voting than Range,.."
>
> That is more true of the "automated approval" version I suggested, and also
> it isn't
> completely clear-cut because Range meets Favourite Betrayal which is
> incompatible
> with Condorcet.
>

Favorite Betrayal in this case means, honest ABC voters who know that A's
losing and that C>B>>A and A>>C>B votes are both relatively common, can vote
BAC to cause a Condorcet tie and perhaps get B to win (if A would win that
tie, then A would be winning already, so they can't get their favorite
through betrayal. In other words, at least it's monotonic.). But if they
bring on the Condorcet tie, they are also risking C winning if there are
more C>>B>A votes than C>B>>A votes. (Of course they're also risking having
been wrong and throwing away an A win, though that's the nature of favorite
betrayal and scarcely bears mentioning.) If they are even considering
favorite betrayal, they probably feel A>B>>C, so even a small risk of C
should be a strong deterrent.

In other words, the whole point of this system is that honesty is the safest
strategy. If voters are even moderately risk-averse and information is
anything less than perfect, the system (and your alternate version proposal)
is, I believe, unparallelled for its strategy resistence. If voters are
risk-seekers and enjoy attempting strategy, then it's no worse than
min(condorcet, approval), which is both IMO implausible and really not too
bad anyway.

Jameson
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