[EM] auto-truncation

[Russ Paielli]

Araucaria Araucana araucaria.araucana-at-gmail.com |EMlist| wrote:

> Consider this case.  Original true preferences:
> 
>   27: A>B
>   24: B>A 
>   49: C
> 
> A is the Condorcet winner.  Now consider what happens if B defects via
> truncation:
> 
>   27: A>B
>   24: B
>   49: C
> 
> Under RP(wv), Beatpath(wv) or DMC, B wins.  B voters have gotten a
> better result by dropping a lower preference.  This is an example of
> the "Later No Hurt" violation of Condorcet completion methods -- B
> voters hurt their favorite by adding a lower-ranked preference.
> 
> But if A puts the approval cutoff above B, B can't win in DMC:
> 
>   27: A>>B
>   24: B
>   49: C
> 
> C wins, anyway you cut it, as you found.  There's no LNHurt situation
> here because B can't win either way.  So the best the B voters can do
> is to add a preference for A.  That's what I mean by the poison pill
> (by the A voters).  Is it clear now?

Ahhh...yes, now I see what you meant. As you pointed out, however, this 
particular situation is apparently no worse for DMC than it is for 
popular (on EM) Condorcet methods (or Approval). Are you saying that, 
with an approval cutoff (i.e., ranking allowed for unapproved 
candidates) that DMC actually has an advantage over those Condorcet 
methods? If so, then I am certainly willing to reconsider allowing an 
approval cutoff.

Note, however, that the added equipment requirement for an approval 
cutoff could delay the adoption for decades, but I won't get into that now.

Let me just suggest another possible approach to the problem: 
auto-truncation. This idea is probably unoriginal, and it is also 
probably meritless, but let just throw it out there anyway as a long 
shot. This idea could be applicable to other methods too, but lets just 
consider DMC/RAV.

Suppose we determine a tentative winner using the standard DMC rules. 
Now we "suppress" (tentatively eliminate) all the non-first-choice votes 
for that tentative winner, then determine a new winner. For all the 
voters who had the new winner ranked above the previous tentative 
winner, keep that previous winner "suppressed", but for all who didn't, 
unsuppress (restore) the votes for the previous winner. Repeat until the 
process converges to a stable winner.

Will this procedure always converge? If so, has it been proposed before, 
and is it equivalent to some other, perhaps simpler, method?


> So a good DMC strategy is
> 
>    Rank all candidates you are willing to see elected, from your
>    favorite to your "hold-your-nose-and-swallow-just-barely-tolerated"
>    candidate.

Why not just go all the way down?

>    Put your approval cutoff just below the candidate with the best
>    shot at winning.  (I think this is Forest's Approval voting
>    criterion).
> 
> Here, that means that the A voters cutoff below A.
> 
> B voters, realizing this is the strategy, will add a lower preference
> for A.
> 
> C voters, if they realize they're in the minority, might then decide
> to rank their preferred opposition alternative below the cutoff.  If
> they despise A, they might actually vote for B in sufficient numbers
> to turn the election around.
> 
> But you don't get this effect if you remove the approval cutoff.
> 
> 
>>Those schemes might or might not be acceptable. I realize they seem
>>very simple to you, but I think they may still be too complicated
>>for major public elections. Also, I don't like the idea of requiring
>>the voter to actually write a number. That's asking for trouble
>>because the written number will sometimes be ambiguous.
> 
> 
> I find writing a number to be much faster than filling in an optical
> cell!

I don't think optical cells are the answer either. What you want is a 
nice, simple touch-screen (or mouse based) system. And yes, of course 
you need to generate paper ballots too.

> 
>>I envision something like the Graphical Voter Interface (GVI
>>http://ElectionMethods.org/GVI.htm) that I developed a while back
> 
> 
> Can't see the screenshots:
> 
>   Permission Denied
> 
>   The area you are trying to access has been closed off by the server
>   administrator.

OK, I fixed it. Take a look at it.

> 
> 
>>just for kicks. It has a column of buttons, each about a half inch
>>high by 3 inches wide, with a candidate's name and party on each
>>one. You select them in order of preference by simply touching them
>>on a touchscreen (or clicking on them with a mouse on a conventional
>>monitor). You can always backtrack, of course. You can specify equal
>>rankings by touching a selected candidate a second time (GVI doesn't
>>currently allow that, but it could be added).
> 
> 
> Woowee.  Screen takeover.  Watch those colors and fonts!

I don't understand what you mean by "Screen takeover."

> I'm not sure I find that more intuitive.
> 
> Anyway, I favor paper ballot counting, period.  Machines would be used
> only for assistance.  What does your software do then?

Yes, GVI can print paper ballots. However, this feature is just a 
prototype. it just prints the ballot to a conventional printer.

--Russ