[EM] Smith, FPP fails Minimal Defense and Clone-Winner

Juho juho4880 at yahoo.co.uk
Wed Mar 10 13:24:32 PST 2010

On Mar 10, 2010, at 7:26 PM, Kristofer Munsterhjelm wrote:

> Juho wrote:
>> On Mar 10, 2010, at 7:08 AM, robert bristow-johnson wrote:
>>> so, keeping RP, Schulze in mind for later, what would be a "good"  
>>> scheme for resolving cycles by use of elimination of candidates?   
>>> what would be a "good" (that is resistant to more anomalies) and  
>>> simple method to identify the "weakest candidate" (in the Smith  
>>> set) to eliminate and run the beats-all tabulation again? i'm not  
>>> saying elimination is a good way to do it, but it might be easier  
>>> to sell to neanderthal voters.
>> All methods have some weaknesses that can be used against them in  
>> the marketing battle. So maybe the challenge is to build a solid  
>> campaign that is convincing enough to neutralize all emerging fears  
>> and failure examples.
>> Schulze method is quite convincing since it is already in use in  
>> many places. (I'm not sure it is objectively better than ranked  
>> pairs and others although it is certainly a good method.) Ranked  
>> pairs can be easily described as a method that sequentially  
>> confirms pairwise wins, so it is almost as natural and straight  
>> forward sequential algorithm based as IRV (although it is a bit  
>> more complex in the sense that it compares pairs instead of single  
>> candidates when making the sequential decisions). And there are  
>> also simpler Condorcet methods like minmax(margins) that simply  
>> counts the number of additional votes each candidate would need to  
>> beat all others.
> For Schulze, I think the strategy should make use of its current  
> popularity (relative to other Condorcet methods, at least). Maybe  
> make Condorcet programs and patches to widen its use among those who  
> know computers, and encourage organizations to use Schulze for their  
> internal decisions (like the Pirate Party did with its primaries,  
> although that's not quite the ideal usage of the system).
>> I'm not aware of any sequential candidate elimination based method  
>> that I'd be happy to recommend. One can however describe e.g.  
>> minmax(margins) in that way. Eliminate the candidate that is worst  
>> in the sense that it would need most additional votes to win  
>> others, then the next etc. In the elimination process one would  
>> consider also losses to candidates that have already been  
>> eliminated (I wonder if this approach makes it less "natural  
>> looking" than the elimination process of IRV).
> To my knowledge, Schulze-elimination is the same as basic Schulze.  
> In other words, if you run Schulze, eliminate the loser, run it  
> again, etc, you end up with the original result. That's not very  
> useful, but still...
> It might also be that any "full-blown candidate elimination  
> method" (you run the election as if the one that was eliminated  
> never stood) with a weighted positional base method (Borda,  
> Plurality, ...) is nonmonotonic. I can't prove it though!

One more addition to this elimination discussion. Maybe ability to  
give an ordering of the candidates is more important (and more  
generic) than using an elimination process. The preference graphs that  
many Condorcet methods use may not be as easy to understand to the  
voters as plain ordering is.

In principle single winner methods need not be able to produce any  
ordering of the candidates. It is enough to pick the single winner.  
But in order to make it easy to the voters and candidates to  
understand the results (and to explain e.g. how close some candidate  
was to winning the election) good and simple graphical and numeric  
information may be valuable in practical elections.

>> But as said, maybe the key is to arrange a solid campaign. You can  
>> surely e.g. find lots of election method experts that are happy to  
>> agree that Condorcet methods are the best for some city for some  
>> need and best single winner methods (for competitive elections) in  
>> general. But quite certainly there will be also experts that think  
>> otherwise. And there is certainly a risk that all the Condorcet  
>> friendly experts will use different argumentation, may disagree on  
>> details and as a result will confuse the audience. Maybe one should  
>> start from Scientific American etc. to first firmly establish the  
>> idea that Condorcet methods indeed are the de facto state of art  
>> methods (and practical too). IRV campaigns have been successful, so  
>> I wonder why Condorcet campaigns could not follow (maybe Burlington  
>> needs a timeout now but not much more, and other cities could take  
>> steps forward already now and support Burlington that way).
> The first step would be to say: okay, there are many Condorcet  
> methods, but they differ in fine tuning. For public elections, good  
> enough is good enough, and let's pick one that's good, then unify  
> around it. That method could be RP or it could be Schulze, or  
> something else (I think independence from Pareto-dominated  
> alternatives would be nice, but at some point we'll just have to say  
> "good enough").
> I mention RP and Schulze in particular because RP is easy to explain  
> (relatively, given the criteria it passes), and Schulze has some  
> record of use.
> So does, say, Copeland, but in my opinion, it isn't "good enough".  
> The iterated Copeland(2,1) version may be better, but probably isn't  
> cloneproof.. and so on.
>> (I have to add that if people want to keep the USA as it mostly is,  
>> a two party based system, then I must recommend FPTP :-). And if  
>> not, then maybe also some additional (maybe proportionality  
>> related) reforms are needed.)
> Wouldn't something like Condorcet multiwinner districts be better?  
> Pick a good Condorcet method and send the 5 first ranked on its  
> social ordering to the legislature. That would pick a bunch of  
> centrists (thus have "stability"), but it would pick the centrists  
> people actually wanted.
> Hm, that might not provide a true two-party system, though. One  
> could also have a "PR" system where the number of votes is weighted  
> so that parties with broad support gain superproportional power, but  
> then the question becomes why one should bother with the PR at all.

Maybe Condorcet + single winner districts is a more stable approach.  
That combination makes a two-party system just somewhat softer, and  
allows the party structure (in individual districts) to evolve in time.

Another approach to systems between proportional representation and  
the two-party approach could be to have a proportional method but use  
districts with only very few representatives (2, 3,...). That would  
provide rough but in principle accurate proportionality and still give  
space only to few major parties. (Obviously my definition of full  
proportionality must be "with 1/n of the votes you will get one seat  
(where n = number of representatives)".)


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