[EM] Re: Citation for immunity to strategic voting?

[Rob LeGrand]

Andrew Myers wrote:
> I'm writing a short paper on secure implementations of Condorcet
> voting.  I would like to claim that Condorcet methods are immune
> to strategic voting when there is a Condorcet winner (that is,
> voters cannot improve the election result from their perspective
> by voting insincerely).

I wish that were true.  But sometimes a Condorcet election can be
manipulated by creating a cycle where none existed before.  Here's
one example:

45:R>A>C
20:A>C>R
35:C>A>R

A is the Condorcet winner and wins.  But if the C>A>R voters
strategize:

45:R>A>C
20:A>C>R
35:C>R>A

a A>C>R>A cycle results.  Some Condorcet methods, like Baldwin
(Borda-elimination) and Arrow-Raynaud (minimax-elimination), now
give C as the winner.

I'm sure someone else will post a more compelling example.

--
Rob LeGrand, psephologist
rob at approvalvoting.org
Citizens for Approval Voting
http://www.approvalvoting.org/

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