[EM] Re: Empirical data on cycles

[Rob LeGrand]

Adam Tarr wrote:
> It suggests to me that _natural_ cycles are very rare. This does
> not automatically mean that cycles can never be a problem. The
> important thing is to pick a Condorcet method where, when a
> Condorcet winner exists in sincere preference, it is extremely
> rare than any faction has a tactic where they can cause a
> favorable cycle. (I am referring, of course, to winning votes.)

Any such cycle-creating strategy that exists under a margins method
also exists under the equivalent winning-votes method.  If the
margins strategy includes no equal ranking, the strategies are the
same.  If it includes equal ranking, such as changing sincere

20:A>B>C>D

ballots to

20:A=B>D>C

ballots, an equally successful winning-votes strategy would be

10:A>B>D>C
10:B>A>D>C

So such situations are no rarer under winning-votes than under
margins.  If anything, it seems to me that winning-votes might
provide more such opportunities to the strategic voter since equal
ranking has no effective equivalent under margins.  (But it's
usually more effective just to order-reverse anyway.)  It is for
this reason and the fact that winning-votes encourages equal ranks
near the top of the ballot and full ranking near the bottom even
when insincere (and even in the zero-info case!) that I prefer
margins to winning-votes.

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

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