[EM] Confirmed!: Condorcet efficiency of IRV > 2-stage runoff

[Forest Simmons]

Unless I am much mistaken, these simulations are based on the assumption
that the voted ballots are sincere preferences, i.e. "zero
information" about the candidate chances of winning, i.e. no strategic
considerations.

As I remember, the context of Steve Barney's original question was a
discussion of manipulability, which requires the use of strategy based on
at least partial information (or misinformation).

This reminds me of another question that I've been wondering about. Does
anybody know of an example in which IRV would give a superior result to
ordinary lone mark plurality in the case of near perfect information,
assuming the use of near optimal strategy by the voters in both cases?

Forest

On Wed, 18 Sep 2002, Bart Ingles wrote:

>
> This is in Merrill's book as well:
>
> Making Multicandidate Elections More Democratic
> Samuel Merrill, III
> Princeton University Press, 1988
>
> It's out of print, but can be tracked down through public or university
> libraries via Inter-Library Loan.
>
> The book includes several other election methods, and other scenarios
> besides random profiles.
>
> Hare seems to deteriorate a little more slowly than Runoff when the
> number of candidates goes up, but still declines substantially.  And
> both "crash" when the candidates are more clustered than the voters.
> Plurality was even worse on both counts.  The other methods were better.
>
> Bart
>
>
> Steve Barney wrote:
> >
> > I've discovered a professional article on voting theory which seems
> > to confirm my argument (see
> > <http://groups.yahoo.com/group/election-methods-list/message/9057>)
> > 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)
> >
> > Notice that, just as I surmised, the two methods start out equivalent
> > with 2 or 3 candidates, and then the IRV does better and better than
> > the 2-stage runoff as the number of candidates grows.
> >
> > Also, on a lighter note, this article cites this list in footnote 9
> > on page 6:
> >
> > 9 "We use the name “Baldwin” rule in order to stress the difference
> > with the Nanson rule. John Taplin mentioned that name on the Election
> > Methods Internet Site. The procedure may be better known as e.g.
> > Nanson’s modification of his own rule (cf. McLean and Urken (1995)),
> > but this terminology is confusing."
> >
> > =====
> > Richard M. Hare, 1919 - 2002, In Memoriam, http://www.petersingerlinks.com/hare.htm
> >
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