Hi Kristofer, thanks for the answer
2012/10/4 Kristofer Munsterhjelm <[email protected]> > On 10/04/2012 07:05 PM, Peter Zbornik wrote: > >> Dear all, >> >> A simple extention of IRV to two rounds IRV would be the following: >> 1. In the first round have no quota (i.e. no transfer of surpluses). >> 2. The two candidates who are eliminated last go to the second round >> 3. In the second round the two candidates meet in a normal IRV election. >> >> Question: Will this method always generate the same winner as one-round >> IRV, in the case that the preference orderings of the voters are the >> same in both rounds? >> I believe yes and it seems trivial, but cannot prove it just like that. >> > > Yes, at least if you disregard ties. Say that after every round but the > last has been run, A and B remain. Then A will win in IRV iff a majority of > the ballots that express a difference between A and B, ranks A above B. Now > consider a genuine runoff between A and B. The voters can only give their > vote for either A or B (or abstain), and if the majority interested in that > contest votes for A, then A wins, and same for B. Since the preference > orderings are the same, this A-vs-B contest is also the same as in the > final round of IRV. > > > I am considering proposing this method for use among the Czech Greens as >> an improved IRV and a natural two-round alternative to the Run-off >> elections we use today. >> > > It might be better than Plurality runoff - I haven't heard of anybody > using IRV+runoffs before, so I don't know its performance for sure. > > If you're looking at variants of IRV, you could ensure the CW stays in the > contest (when there is one) by not eliminating the Plurality loser at each > stage of IRV, but the one who loses a one-on-one between the two candidates > with least Plurality score for the round in question. That may be of use if > you want to have a runoff and at the same time make sure the Condorcet > winner stays in it. > > I guess it is the simplest transfer from IRV to Condorcet voting. And this recent paper in Voting Matters on Hybrid methods show it might be a good method to use, which is robust to strategic voting. At the same time it is very simple to describe. Condorcet methods are not requested in my party yet, but I like this Condorcet-light method and will consider it when time is rights. P.
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