[EM] Spoilers

[Anthony Simmons]

>> From: "Tom Ruen" <tomruen at itascacg.com>
>> Subject: [EM] Election results and analysis:
>>   What are your favorite months?

>> Without runoffs, our elections with 3 or more
>> choices often have a "spoiler candidate" where
>> if people vote for a 3rd party favorite, this
>> may help their least favorite win. Therefore
>> voters with an acceptable compromise candidate
>> are encouraged (through fear) to vote for
>> their compromise (who is among the expected
>> top two candidates) to have a positive affect
>> on the election results.

>> Approval allow voters to vote BOTH for a most
>> favorite AND a compromise, if they are worried
>> their favorite won't win. This can be very
>> important for 3rd parties who need a certain
>> fraction of the vote in order to qualify for
>> governmental funding, and it helps determine a
>> candidate with majority preference in a single
>> election.

This brought up a question for me.  Suppose a
purely hypothetical Approval election in which
there are two major parties, with candidates
Mickey and Goofy.  A third party candidate,
Roadrunner, is very popular, but is not expected
to win.

Roadrunner voters feel they should vote for
Mickey in addition to their own bird, since if
Roadrunner doesn't win, they absolutely don't
want the election going to Goofy.  So most
Roadrunner voters vote for Mickey too.

On the other hand, Mickey voters think that if
support for Goofy is so strong that he beats
Mickey, then for sure he will beat Roadrunner
too.  Thus, they figure that they shouldn't vote
for Roadrunner, since that could build up support
for Roadrunner to the point where, if Goofy
doesn't win after all, the election could go to
Roadrunner.

The end result is that Mickey's perceived
advantage over Roadrunner might get him elected
even though Roadrunner might actually have more
sincere approval than Mickey.

Doesn't this sound a lot like the way Plurality
and IRV suppress support for a third party by
forcing voters to be insincere?