[EM] Burlington VT reconsidering IRV 10 years after IRV failed to elect the Condorcet Winner

[C.Benham]

> Warren has written a bit about it here: https://rangevoting.org/BtrIrv.html
>
> (He states that every Condorcet method fails mono-add-top, which I don't
> think is true, but his example does show that BTR-IRV fails mono-add-top.)

All Smith methods fail mono-add-top, but  MinMax Margins meets both 
Condorcet and mono-add-top.

(One of it's alternative algorithms is just elect the candidate who 
needs the fewest extra bullet votes to
be the CW.)

But looking at that link I saw something different:
> Like IRV, it suffers from "add-top failure 
> <https://rangevoting.org/AddTopFail.html>."

Of course IRV meets mono-add-top.  A candidate can only be eliminated by 
having a shortage of top-rankings.
No ballot's lower rankings can have any bearing on the result until the 
higher-ranked candidates have been
eliminated.

So if X is winning and then we add some ballots with X voted top, X 
cannot possibly be harmed if the method
is IRV.

Chris Benham


On 7/12/2019 9:52 am, Kristofer Munsterhjelm wrote:
> On 06/12/2019 13.48, fdpk69p6uq at snkmail.com wrote:
>
>> Has BTR-STV been used in the real world or analyzed academically?  There
>> are only two sentences about it on Electowiki.
> Warren has written a bit about it here: https://rangevoting.org/BtrIrv.html
>
> (He states that every Condorcet method fails mono-add-top, which I don't
> think is true, but his example does show that BTR-IRV fails mono-add-top.)
>
> On a funny note, a dance contest program on TV here uses a judging
> method that could be seen as a variant of BTR-IRV (if you're willing to
> be very generous). It works like this:
>
> At the end of each program, the judges provide their rating of the
> contestants, and then the callers provide their rating by number of
> calls and web votes. Those are combined to produce an overall rating,
> and then the two bottom contestants do a repetition of their dances,
> during which the callers vote on who gets to continue on to the next
> program and who is eliminated.
>
> It's "like" BTR-IRV since there's a ranking, and the bottom two are
> subject to a runoff, and the loser of the runoff is eliminated. But it's
> a real runoff (not instant), and the initial "round" (program)'s ranking
> is based on ratings, not on first preferences.
>
> I don't think BTR-IRV has been used in public elections anywhere, unlike
> Borda-elimination (as you point out below).
>
>> I know Nanson/Baldwin methods have both going for them, and they're
>> Condorcet and relatively simple to explain to someone familiar with IRV:
>> "Instead of eliminating the candidate with the least number of
>> first-preference votes (which results in vote-splitting and discards
>> some voters' preferences), you eliminate the candidate with the worst
>> average ranking."
>>
>>
>> "In contrast to the Borda rule, our experiments with Baldwin’s and
>> Nanson’s rules demonstrate that both of them are often more difficult to
>> manipulate in practice. These results suggest that elimination style
>> voting rules deserve further
>> study." http://dx.doi.org/10.1016/j.artint.2014.07.005
> James Green-Armytage's paper on strategic resistance seems to put
> Nanson/Baldwin around the same manipulability level as Minmax.
> http://jamesgreenarmytage.com/strategy-utility.pdf page 18.
> ----
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