>Robla: As I recall from discussions on this list, there are plenty of simulations that show that IRV elections tend to resolve to two clusters away from the political center (i.e. two-party system) thus not bucking Duverger's Law any better than plurality. The fact that this happens in the real world is not a surprise, given the theoretical results. In fact, if I recall correctly, it's been shown that IRV tends to reward more extreme candidates over time than plurality does.
However, the simulations show that this doesn't happen for Condorcet methods. They tend to resolve to the center, as do Approval and Range, for that matter. I can't remember who it was that ran the numbers, but hopefully they are reading now (or someone who remembers is reading now) and will chime in with more details on this. Regardless, the fact that real-world IRV elections result in two-party systems is unconvincing evidence that the same would hold true for Condorcet methods. --WDS: This is a very interesting claim. I would be very interested to learn about whatever lies behind this claim that Condorcet does not lead to 2-party domination while IRV does. In IRV it often is not the case that the best strategy is to exaggerate and rank the 2 perceived frontrunners max and min. But nevertheless it sometimes is the case, and a lot of members of Joe Public will do it regardless of what the best strategy is. If enough members of Joe Public do this, then 3rd parties can never win under IRV. I conjectured that this was the reason, or at least part of the reason, that IRV countries are 2-party dominated just like plurality. Now the above paragraph is completely true if everywhere you see the word IRV you substitute the word "Condorcet Method", except for the caveat that there are no Condorcet countries. This suggests to me, but does not fully convince me, that the exact same thing would happen under Condorcet. This is an important question. I in fact am the author of one theoretical study re IRV and 2-party-ization, http://math.temple.edu/~wds/homepage/works.html #76. However that study did not consider Condorcet since at the time I was not under the impression anybody was seriously proposing it for actual use - I was trying to focus on Borda, AV, and IRV. If anybody reworks my arguments to put in Condorcet also, then I will be interested to see that. You are warned it is a bit tricky and I managed to make some stupid errors in this study, which in fact were pointed out to me by some people on EM. The known errors are now fixed in the URL I just gave and the pointer-outers are credited. This theoretical study lived within a rather simplified model of the world and hence maybe is not so relevant to reality, but we do what we can. ---- Election-methods mailing list - see http://electorama.com/em for list info
