[EM] Better runoffs

[Peter Zbornik]

Hi Kristofer,

thanks for the answer

2012/10/4 Kristofer Munsterhjelm <km_elmet at lavabit.com>

> 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.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.electorama.com/pipermail/election-methods-electorama.com/attachments/20121005/b41b5e0b/attachment-0004.htm>