I have a rather practical approach to strategies. Often we talk about theoretical properties of the methods. I prefer talking about the practical impacts (of the known theoretical vulnerabilities) since often the theoretical cases talk only about some marginal cases. I'll explain more below.
Schulze and Condorcet methods in general may sometimes be vulnerable to strategies where voters change some ">" to "=". You however did not present and I do not know situations where it would be beneficial (strategically) to generally vote in approval style in Schulze/Condorcet. My practical approach is such that when some theoretical vulnerability has been identified I try to construct also a practical example (in some well defined real life environment) to see if it really is a threat. One needs to understand also the dynamics of the problem in real life situations. Topics to consider: - how often does the vulnerability occur - what information do the voters have - is that information reliable - unreliable polls - opinions may change - can voters apply the strategy on their own - media or party guidance may be needed - maybe a general rule for all elections - does the strategy require coordination - agreed voting pattern - different strategists to vote in different ways - will others know about the planned strategy - are there counter-strategies? - how "bad" is the change in the outcome - can the strategy backfire There are also many society related aspects: - what are the impacts of strategy proposals - all become strategic? - strategists will lose support? - what is the tradition of the society - strategic vs. sincere - is strategic voting morally acceptable - are the voter opinions stable or changing - party loyalty - are the polls used as propaganda - is the election large or small - do the voters make independent decisions - or do they follow party guidance - number of candidates and parties and groupings - great variety of opinions vs. just few patterns - impact on the next elections and society - e.g. strategic votes to unwanted candidates Practically all methods have vulnerabilities, so we just need to pick methods that are good enough in the given environment. One should also note that often there is also the other side of the coin. When defending against one threat one may open doors to other threats or otherwise make the system worse. (Note that this also means that sometimes it is better to have numerous weak vulnerabilities rather than only one more serious vulnerability, i.e. just listing the individual vulnerabilities does not work.) (One should btw also make sure that the behaviour of the used method can be justified also with sincere votes. Electing a "wrong" candidate with sincere votes is about as bad as electing a wrong candidate due to strategic voting.) Based on this kind of checklists I think it is often quite easy to quickly come into conclusion on if the discussed vulnerability is a serious threat or just theoretical. The theoretical vulnerabilities are important as a basis of the studies but often practical examples of typical but bad situations that may occur in the given environment demonstrate better what the actual performance level of some proposed system is. Practical group strategies that can be applied by individuals without central coordination are the most interesting ones. Counter strategies are already much less interesting (things are already quite bad if people really start using them). Now back to the discussed methods. It is characteristic to Schulze and Condorcet methods that their vulnerabilities are severe in the sense that in some cases some group may indeed (at least in theory) change the outcome of the election, but those strategies are not very easy to identify, not very common and may easily backfire. As a general rule voters' best strategy is often to vote sincerely. In Range one big problem is that exaggeration seems to work quite generally. For example in a typical US presidential election a general recommendation of all Democrats to vote D=max R=min is not a bad strategy to follow. In Condorcet finding a working strategy (other than sincerity) that could be generally recommended to the voters would not be that easy. Juho --- On Tue, 9/6/09, Warren Smith <warren....@gmail.com> wrote: > One problem is nobody really has a > good understanding of what good strategy is. > > If one believes that range voting becomes approval voting > in the > presence of strategic voters (often, anyhow)... > > One might similarly speculate that > strategic voters in a system such as Schilze beatpaths > ALLOWING ballots > with both > and = (e.g. A>B=C=D>E=F is a legal > ballot) usually the > strategic vote > is "approval style" i.e. of form A=B=C>D=E=F, say, with > just ONE ">". > One might then speculate that Schulze, just like range, > then becomes > equivalent to approval voting for strategic voters. > > Well... how true or false is > that? Is Schulze with approval-style > ballots > a better or worse voting system than plain approval? > > How true is it that approval-style voting is "strategic" > for Schulze? > > I'd like to hear people's ideas on this question. > (And not > necessarily just for "Schulze" -- substitute other methods > too, if you > prefer.) > > The trouble is, range voting is simple. Simple enough that > you can > reach a pretty full understanding of what strategic range > voting is. > (Which is not at all trivial, > but it can pretty much be done.) In contrast, a lot of > Condorcet > systems including Schulze are complicated. Complicated > enough that > making confident statements > about their behavior with strtagic voters (or even > undertsnading what > strtagy IS) is > hard. > > Frankly, I've heard various vague but confident claims > about strategy > for Schulze & the like, and my impression is those > making the claims > know very little about what they > are talking about. I also know very little on this, > the difference is > I admit it :) > > > -- > Warren D. Smith > http://RangeVoting.org <-- add your > endorsement (by clicking > "endorse" as 1st step) > and > math.temple.edu/~wds/homepage/works.html > ---- > Election-Methods mailing list - see http://electorama.com/em for list info > ---- Election-Methods mailing list - see http://electorama.com/em for list info