[EM] Runoff vs IRV

[Markus Schulze]

Hallo,

this "IRV vs. Top-2 Runoff" discussion appears every few
months on this mailing list. Therefore, I only list those
reasons why I prefer IRV to Top-2 Runoff:

1) IRV satisfies independence of clones.
2) IRV satisfies majority for solid coalitions.
3) IRV has a higher Condorcet efficiency than Top-2 Runoff.

Steve Barney wrote ("Confirmed!: Condorcet efficiency
of IRV > 2-stage runoff"; 18 Sep 2002):

> I've discovered a professional article on voting theory which
> seems to confirm my argument that the IRV is more likely to
> elect a Condorcet candidate when one exists (with sincere
> votes) than the two-stage runoff procedure (assuming that the
> preferences remain fixed from one stage to the next). Here
> is an excerpt from Table 1, page 6 (in this article, IRV is
> called the "Hare" method):
>
> Table 1: Condorcet efficiencies for a random profile with 25
> voters by Merrill (1984)
> procedure \ # alternatives 2 3 4 5 7 10
> RUNOFF 100,0 96,2 90,1 83,6 73,5 61,3
> HARE (TIES) 100,0 96,2 92,7 89,1 84,8 77,9
>
> See pg 6 of the article:
>
> "Analysis of voting procedures in one-seat elections:
> Condorcet efficiency and Borda efficiency"
> DIMITRI VANDERCRUYSSEN (KUL)1
> March 1999
> <http://citeseer.nj.nec.com/vandercruyssen99analysis.html>
>
> That article notes that this "far-famed table" comes from
> an earlier article:
> Merrill, S., III (1984) “A Comparison of Efficiency of
> Multialternative Electoral Systems”, American Journal of
> Political Science, Vol 28, Issue 1, pp. 23-48.
> (available in the "JSTOR" academic database)

Markus Schulze