[EM] One scenario, many methods, by strategies in final poll

[Jameson Quinn]

2011/3/18 Kevin Venzke <stepjak at yahoo.fr>

> Hi Jameson,
>
> --- En date de : *Ven 18.3.11, Jameson Quinn <jameson.quinn at gmail.com>* a
> écrit :
>
>
> Great results.
>
> I think it would help if you gave the SCWE of each method above the table,
> and the SCWE of each line after that line. That way, we could see which
> strategies were causing the problems with SCWE. Also, if you give further
> scenarios, it would be great to see the results sorted by SCWE.
>
> Well, I tried to sort them thematically this time. I wasn't going to
> discuss scores at all
> at first, as there are just too many things I could say.
>
> One thing that strikes me is that often the methods with strategy
> vulnerabilities were
> better anyway, in this scenario. Sincerity doesn't necessarily translate
> to quality.
>

Would you say that that holds for dishonest strategies (C, B) or only
semi-honest ones (M, T)?


>
> I can understand wanting to understand the outcome of each "line" though...
> I'll have
> to think about that.
>
>
> I would be interested to see results for MCA runoff methods with this. The
> possibilities are:
> MCA-Runoff-approval - runoff if tied median, two candidates with highest
> portion at median advance (or highest approvals if failed majorities)
> (I suspect the top result for this would be ---TTTT, with very high SCWE)
>
> MCA-Runoff-preferred - as above, two winning candidates with highest top
> ranking advance.
> (I suspect that the top result would be MMMTTTT, with high SCWE)
>
>
> Ok, I can add these. I think there is a large Condorcet advantage to the
> runoff methods.
> I do wonder about the clone issue though. It won't show up in this setting,
> but if there
> were no candidate limit candidates might end up nominated in pairs.
>

These methods do have a problem with clones. That's why I came up with the
MCA-Asset methods; I think they'd do better against clones.

>
>
> Both of those systems will generally agree with the corresponding MCA-Asset
> version. The exception is that MCA-Asset will almost always elect C if B is
> eliminated (ineligible for transfers), while MCA-Runoff will tend to elect A
> in that situation. That's  because B will transfer votes to C even though
> some of those original voters might have preferred the less-extreme A. Since
> both of these results are probably Condorcet failures anyway, the only
> important difference resulting would be if under MCA-Asset, C voters were
> more inclined to truncate, while under MCA-Runoff, A voters would do so.
> However, since the other side always has a defense, I don't think either of
> those would hurt the SCWE. Still, it might be worth simulating MCA asset
> (assuming that B would always choose to transfer votes to C, and C and A to
> B; and that A would transfer votes to B if they could and C couldn't, that
> is, that A would believe the implicit threat of B to transfer to C.)
>
>
> It is probably possible to do this for spectrum-based scenarios. I can't
> remember
> what the conditions are for this to happen under that method; I wonder if
> you have it
> handy.
>

By "this", I assume you mean vote transfers? If there is a median tie, then
candidates can "transfer" their votes to to any other candidate who has a
higher [stat of interest], where stat of interest is defined as Preferrals
(see runoff-preferred) or Approvals (see runoff-approved). If A transfers to
B, all ballots count B at max(A,B). If this does not resolve the election,
then the winner is the member of the post-transfer tie with the highest
post-transfer stat of interest.

I believe you could use "asset" for any scenario, by assuming that the
candidate's preferences are the same as those of the average of the voters
who rank that candidate top.


> If you're adding in these methods, you should add Majority Judgement as
> well (eliminate median votes to break ties). This would probably come out
> the same as MCA, but it is not quite identical, so it would be good to
> confirm that.
>
> I'm not sure I have understood how this method works. Can you describe it?
>

Say A gets (Preferred/approved/unapproved) (20/50/30) and B gets (30/30/40).
Both are median approved. Eliminate 20 median votes from each and you get
(20/40/30) for A - still median approved - but (30/10/40) for B - rounding
down, that's median unapproved. So A wins. (Note, elimination can shift
median in either direction to break the tie.)

This is not my proposal, but the idea from the book Majority Judgement.


>  Anyway. As to your actual results, it seems to me that the "good" methods
> are the ones above 95%. Out of that set, it seems to me that it's clear that
> MCA and Bucklin are the simplest methods to explain to voters. (Of course,
> the MCA-runoff and -asset methods I propose are complex, not simple).
>
> So, I'd like to see someone make a good argument against MCA being the best
> practical single-winner reform, for combination of simplicity and strategy
> resistance. There may be such an argument which I'm just too biased to see.
> If not... well, all y'all can unite under my banner at last :).
>
>
> Well, we need to do more scenarios. I don't know if my first post, around a
> week ago,
> made it to the list. But (assuming I'm looking at the right Excel file at
> the moment)
> MCA placed fifteenth there, after methods like DMC and margins.
>
> In a non-spectrum-based set of trials, MCA was bottom half. The best SCWE
> was
> actually TTR. I tend to think the quality of MCA etc. depends on the voter
> preferences
> being distributed in a certain way. If presence or absence of a top-slot
> majority doesn't
> inform much in the given scenario, it will boil down to Approval.
>
> Plus sincere Condorcet efficiency is just one thing. We could talk about
> election of
> utility maximizers, average utility, Condorcet losers, utility minimizers.
>

With all voters strategic, I believe the first two of those metrics will
just be noisier versions of SCWE. (I don't know, or honestly care much,
about the latter two "worst-case" metrics, because I think they will be
acceptably small under the methods I care about.)


> I'm also
> concerned about the possibility that some methods just won't support three
> candidates
> in practice. That may not be relevant to MCA though.
>
> My initial bets are on AWP implicit because I don't remember ever seeing it
> place badly,
> so far.
>

Very interesting. Do you think AWP-implicit-minimax is an acceptable
substitute for beatpath, etc? (Because AWP is tough enough to describe with
just minimax). And have you tried 3-rating CWP? My feeling is that 3-rating
levels is sometimes the sweet spot, like 2 and infinity, and unlike any
other number.

Jameson
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20110318/60d1d0df/attachment-0004.htm>