[EM] Voting Benchmark

[Kevin Venzke]

Hi Marijn,
Yes, a few thoughts:1. The path tracing (propagation of votes through paths) may seem odd, and it does create problems if you want to create guarantees about the effect of a given ballot (like LNHarm or FBC). But path tracing can provide a useful framework for resolving clone situations or Condorcet cycles. I'd note also that the problem of "voting A>B can help C" is a problem common to many or most election methods.2. Regarding sensitivity to a small change in votes: I would suggest that this is true even with a two-way FPP election: a contest's win vs. loss is the most important thing, and considering the strength of the win at all is a novelty. But it's an interesting question, whether the single-direction flow of votes creates more tactical voting opportunities.3. I call Schulze with votes flowing in both directions "Schulze(pairwise opposition)." The results can be less decisive. For example, suppose that candidate A has 45% of the vote (bullet votes, no lower preferences), and the rest of the votes are some combination of B, C, B>C, and C>B votes. Say there is an A>C>B>A cycle. It's likely that B and C will tie for the win because each received their greatest opposition from A. Whatever tiebreaker rule is used, if it elects C, and C has fewer preferences in total than A's 45% in first preferences, that would violate the Plurality criterion. Some of us would find that to be a bad outcome (i.e. hard to defend), so you may want to consider it.
Kevin

      De : Marijn Stollenga <m.stollenga at gmail.com>
 À : Kevin Venzke <stepjak at yahoo.fr>; "election-methods at lists.electorama.com" <election-methods at lists.electorama.com> 
 Envoyé le : Jeudi 1 octobre 2015 4h21
 Objet : Re: [EM] Voting Benchmark
   
 Yes, actually my main motivation was the strange properties in Schulze that I didn't like. 
 Firstly, the propagation of votes through beaten path sounds interesting, but it is also pretty strange. By voting a dominance of A over B, you might end up voting for C if some large other group votes C over A a lot, even if you don't like C at all. This leads to some complex tactical voting.
 
 Secondly, the votes only flow if A over B has more votes than B over A say. On first sight this sounds good but introduces a sensitivity in the method that can completely flip results with a small change of votes, also leading to possible loss of votes and tactical voting. Why can't votes simply flow both directions? In my implementation I tried it and it still led to dominant results in my experiments, but I guess it's needed for certain properties?
 
 Any thoughts?
 
 Marijn
 
 On 30/09/15 14:40, Kevin Venzke wrote:
  


  Hi Marijn, 
  I think you might start with the criteria that motivated Schulze, or criteria that differentiate popular methods. 
  For instance: Schulze: clone independence, monotonicity (mono-raise), Condorcet, Schwartz IRV: clone independence, later-no-harm, later-no-help Approval: participation, favorite betrayal (FBC) 
  Unfortunately it's not necessarily straightforward to demonstrate that a new method satisfies or doesn't satisfy some criterion. 
  Some of us have simulations to attempt to gauge the incentives to use specific strategies (e.g. compromise, truncation, burial). But since simulations are based on the programmer's assumptions, nothing is standardized. 
  My hunch (based on my own experiments from 10+ years ago) is that if Schulze is your original inspiration or standard, and you make your own rank method, you may make something that gives similar results to Schulze, but most likely it won't satisfy all of Schulze's technical criteria. 
  Kevin 
      De : Marijn Stollenga <m.stollenga at gmail.com>
 À : "election-methods at lists.electorama.com" <election-methods at lists.electorama.com> 
 Envoyé le : Mercredi 30 septembre 2015 4h12
 Objet : [EM] Voting Benchmark
   
 Hello,
 
 I am implementing a new election method, after initially playing with 
 Schulze voting. In the process I really want to compare my method to 
 Schulze and other methods according to several types of quality. Is 
 there a good benchmark currently, that I can start from?
 
 Marijn
 
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