Re: Range Voting - the simpler better alternative to Condorcet voting
Sam Hocevar <sam@zoy.org> wrote:
> On Fri, Jun 15, 2007, Barak A. Pearlmutter wrote:
> > You make another point, which is interesting, but which actually
> > when carried to its logical conclusion ends up being in support of
> > Range Voting over Condorcet. If you continue with the logic
> > asking what happens when Range Voting voters vote strategically,
> > you find that in Range Voting where all voters are well informed
> > of the opinions of the electorate in general, and all voters cast
> > optimal strategic ballots, you get approval voting, which results
> > in ... the winner being what would have been the winner of a "100%
> > honest" Condorcet election.
> Unless you can tell us how to be well informed of the opinions of
> the Debian electorate in general, especially with ballots that go
> beyond yes/no questions, yet still want to make a point about the
> Debian voting system, you should not use that assumption in your
> reasoning.
I don't really understand your point here. Under any particular set
of symmetric assumptions people have made, Range Voting seems to
perform better than Condorcet. These are practical assumptions,
rather than theoretical ones. Like: everyone tries to vote
"honestly". Or: some people try to vote "honestly" others try to vote
"strategically" using whatever information they know. Etc.
One limiting case of this is where people think they know who the
front runners are, and many people vote to try to get their preferred
candidate elected. This is behavior you might expect in practice,
right? Under those conditions, Range Voting performs well, and
Condorcet runs into horrible problems. In fact, when people think
they know who the front runners are and are correct, RV with highly
strategic voters leads to electing the honest Condorcet winner! That
shows how very robust RV is to strategic voting. Unlike Condorcet,
which basically falls apart when people act like ... well, like
people.
Certain situations are more mathematically tractable and easier to
explain than others. That is why I talked about that particular
limiting situation in the message you responded to: because it is easy
to see what's going on, and it is interesting. Not because only under
*those* assumptions does RV beat Condorcet. In fact, under all
realistic conditions I've seem discussed, RV seems to beat Condorcet.
But if you have some other actual specific situation in mind where you
think Condorcet would perform well relative to RV, then let's hear it!
(The only situation in which Condorcet beats RV proposed in the
discussion so far is: RV voters voting strategically vs Condorcet
voters voting honestly. When pressed as to why this startling
asymmetry would arise, it's because someone official tells the
voters---incorrectly---that they'd hurt themselves by voting
strategically with Condorcet. That is a pretty outlandish assumption,
and basically goes against human nature: it assumes people won't often
try their best to get their favored candidate elected. And it sort of
contradicts itself, in that the "official instructions to voters" says
something untruthful in order to obtain a better global outcome. In
other words the "official instructions to voters" are themselves
strategic rather than honest! And for some reason, the same
"strategic" instructions to be honest aren't given with RV. And even
under this very silly assumption, Condorcet only beats RV by a tiny
bit.)
--
Barak A. Pearlmutter
Hamilton Institute & Dept Comp Sci, NUI Maynooth, Co. Kildare, Ireland
http://www.bcl.hamilton.ie/~barak/
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