[EM] Defensive strategy for Condorcet methods

[Juho Laatu]

On 8.6.2011, at 16.33, Jameson Quinn wrote:

> It's easy to minimize the problems with one's preferred systems, and focus on the problems with other systems you see as "competing" for mindshare. It's not even dishonest: the truth is that, compared to the giant issues with plurality, any good system has problems that are minor, but that on the other hand such minor problems would still be a hurdle in convincing voters to make a switch.
> 
> But I don't think it's getting us much of anywhere to argue this back and forth.
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> Let's imagine these minimizing-the-issues points were all granted, on all sides. Say Condorcet had negligible strategy, Range strategy were always unbiased, and SODA had no smoky rooms. (I think that all three propositions are close enough to true to use as an approximation.) I think that it's undeniable then that SODA would have the simplest balloting and Range the best results.
> 
> So I, personally, don't see the attraction of Condorcet when compared to other proposals.

I think the attraction of Condorcet methods is in that they 1) can collect very well sincere ranking information, 2) work also in competitive environments, 3) offer a sound basis for majority based elections (Condorcet criterion). Condorcet methods chat can be seen as a major local optimum in the methods space.

Range is a nice method for some environments. It differs from Condorcet methods in 1) since it can not collect sincere ratings reliably, 2) since it has some Approval like problems in competitive elections when the number of potential winners is higher than two (while Condorcet's problems can be claimed to be typically negligible), 3) since it (=sincere ratings) is not majority based. One might consider the "sum of ratings" philosophy to lead to better winners than the "majority decides" philosophy. Even if on prefers the "sum of ratings" philosophy, "majority decides" philosophy could be considered better in competitive elections since one can not expect voters to provide sincere ratings if they have also the ability to decide by majority (as e.g. in two candidate Range elections). Range is thus a nice method, but mainly for environments that are non-competitive and where we want to follow the "sum of ratings" philosophy. This was one argument why Condorcet can be considered to be a clear local optimum in the typically competitive political elections.

In SODA simplicity is one of the main targets. Although it has some nice properties like electing often Condorcet winners and avoiding many strategy and smoke filled room related problems, I'm not sure that it would automatically offer more than Condorcet methods do. Because of its simplicity and its ability to argue benefits over plurality it may be a good candidate in environments that now use plurality.

I.e. all good methods but I still tend to think that for competitive political elections Condorcet methods may provide a quite good local optimum. In Condorcet the ballot filling procedure is more complex than in SODA, but if that is not a problem, then Condorcet might work very well in most typical political elections (maybe the strategy problems will not appear, maybe also that poll related defensive strategy that I mentioned could be used if something strange happens).

> But... I'd rather find a way to agree than fight about it. In my other recent message, I suggested that we put forward SODA and one simple Condorcet method as the practical proposals in some statement which people here could sign on to.

Yes, it would be good to find better agreement on what would be good methods for practical elections. Based on this discussion I see Condorcet methods as good general purpose single-winner methods for competitive environments. Range is good only for certain environments as discussed above. SODA may be good especially when simplicity of the voting procedure is sought.

In SODA I'm most worried about the Approval related problems, maybe also possible trading of votes, but it is an excellent idea and method anyway. In general a good approach when recommending different methods could be to list sincerely the benefits and problems and recommended use for each good method (good = can be considered to be a local optimum in some environments). The list of recommended methods could be a long one, a short one, targeted for certain target audiences or maybe all possible (single-winner and/or multi-winner) environments.

Juho



> 
> Jameson
> 
> 2011/6/8 Juho Laatu <juho4880 at yahoo.co.uk>
> There has been quite a lot of discussion around the strategic vulnerabilities of Condorcet methods on this list recently. In general I think Condorcet methods are one of the least vulnerable to strategies, and in most typical elections their vanilla versions are simply good enough. In the case that people would start voting strategically there is one interesting defensive strategy that has not been discussed very much. The defensive strategy is to not tell your sincere opinions in the polls. Most Condorcet strategies are based on quite accurate understanding on how others are going to vote. If I expect someone to play foul play, I might just refuse to give the required information to them, and recommend others to do the same. (Also giving planned false information to mislead the strategists is possible, but more difficult.)
> 
> This approach does not work about irrational voters that will bury anyway, just in case that might help. But the point is that in Condorcet elections the best strategy, in the absence of good information on the preferences, is to vote sincerely. In real life this strategy could be mentioned as a possibility in the case that strategic voting becomes threatening. The outcome hopefully is such that all parties, experts and media would recommend voters to vote sincerely and not try strategies. That would be better to all than having to live without the interesting polls. What do you think? Is this a way to drive away possible evil spirits and strategy promoting parties, experts and media?
> 
> Juho
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