Dear participants,
Forest Simmons wrote (14 May 2001):
> Here's an inconsistency of IRV that I wish somebody had told me about
> before I submitted my article to the Green Voice: It is possible for
> a candidate to "win" every precinct without winning the election.
Richard Moore wrote (14 May 2001):
> I had thought of this problem once before when thinking about IRV's
> failure to meet the Summability Criterion, but it wasn't on my mind when
> I reviewed your article. Every elimination in IRV means going back to the
> original ballots and eliminating the loser of the round, then recounting
> (you can sum the ballots into bins for each possible combination of votes
> such as A, AB, ABC, ACB, AC, ACD, etc., but this array gets very large
> very quickly as the number of candidates goes up, as we saw here a few
> weeks ago). That means per-precinct vote totals are useless. You have
> to do the elimination globally, not locally, and that means you can't
> predict the results from local data. Even if all localities pick the
> same winner.
Bart Ingles wrote (14 May 2001):
> The property not being met here is actually called "consistency", if
> I'm not mistaken. Approval, Plurality, and Borda are consistent, but
> not many others. Maybe some variants of those three.
Actually, the consistency criterion and the Condorcet criterion are
incompatible.
******
Richard Moore wrote (14 May 2001):
> Another consequence of the summability failure is that reporting IRV
> results will be very complicated. At least for Condorcet you could
> publish the overall pairwise matrix (and also the pairwise matrices for
> individual counties or precincts or whatever the desired resolution is).
I guess that IRV supporters will say that --for a voter to see what his
vote did-- it is sufficient to publish the votes of each IRV step.
Markus Schulze
