[EM] Condorcet Criterion vs. Condorcet Efficiency

[Bart Ingles]

Alex Small wrote:
> ...
> I'm curious if any work has been done comparing the Condorcet efficiencies
> of Approval and IRV.  It's been a few months since I looked at Brams and
> Fishburn, and I don't have a copy handy, so I don't know if they compared
> the two.  When my copy arrives (ordered it used) I'll check it out.

Check out "Making Multicandidate Elections More Democratic"
Samuel Merrill, III
Princeton University Press, 1988

You might be able to find a used copy, or any good university library
should have it.  Any public library should be able to obtain it through
inter-library loan -- I think there was a one-dollar charge when used
this.

Two chapters compare several methods using both Condorcet Efficiency and
Social Utility Efficiency, using random society and spatial models.  One
thing I noticed was that all models assume no strategic information, so
they appear inherently stacked against Approval (Merrill addresses this
in his comments, stating that in a strategic situation Approval should
do better and Condorcet worse than shown).

Still, Approval holds its own, and tends to give moderately high but
consistent results across the board w/ Condorcet efficiency, and very
good results w/ Social Utility.  Plurality, Runoff, and IRV all do
poorly when there are many candidates, or when the candidates are more
centrist than the voters.

Also some of the graphs are scaled differently, so that in cases where
Approval initially doesn't appear to do well, the left-hand scale shows
that the results are all relatively close.  In other graphs, where
runoff and IRV do poorly, the scale shows that they really are abysmal.

Bart

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