I am very happy to see SPI adopt a voting system designed for proportional representation.
However I do feel obligated to correct a simple incorrect statement, namely that STV, a proportional representation system built upon IRV, is in some sense best-of-breed. STV in fact exhibits a variety of very serious pathologies, not just in theory but in actual practice. Even IRV itself exhibits some serious problems, including most troublingly non-monotonicity---meaning that under some not-unusual circumstances changing a ballot to rank a particular candidate *higher* can cause the candidate to go from winning to losing. STV necessarily inherits these pathologies. Although poorly formatted, the following case study of an actual election, the 2009 Burlington Vermont Mayoral election, shows that the IRV system actually used exhibited about the worst imaginable pathology: of the three major candidates, it elected the one who lost head-to-head to each of the other two according to the ballots cast. Details: http://rangevoting.org/Burlington.html Burlington subsequently changed its election system away from IRV. Similar pathologies apparently happened in the IRV 2006 Peru presidential election and the IRV 1970 Chile presidential election. Using the Debian leader election data 2001-2005, in one of those five elections IRV would have given a different winner than the Condorcet method actually used, even though in all cases the Condorcet winner beat all other candidates head-to-head. See http://rangevoting.org/Debian2003.html for details. In another one of the elections there were a variety of IRV pathologies actually exhibited. The most interesting of these to me is that there were two ballots each of which had the property that, had IRV been used, removing that ballot, which prefers A to B, would have changed the winner from B to A. I don't have a dog in this fight. I'm just interested in the math and in Bayesian methods. These have convinced me that Reweighted Range Voting (RRV, http://rangevoting.org/RRV.html) and Asset Voting are the best proportional representation voting systems currently known. And that the problems with STV are not merely academic but occur frequently in real elections. Asset Voting does not seem practical for SPI---although it would be pretty fun. STV (and even IRV) do not come off very well in any of the careful neutral analyses I've seen. --Barak. _______________________________________________ Spi-general mailing list Spi-general@lists.spi-inc.org http://lists.spi-inc.org/listinfo/spi-general
