[EM] Participation IRV badexample

MIKE OSSIPOFF nkklrp at hotmail.com
Sat May 6 23:56:47 PDT 2000

EM list--

My standard 3-candidate IRV badexample works fine to show
IRV's failure of Participation, if I temporarily remove some
of the C voters:

40: ABC
25: B
20: CBA

C gets eliminated & transfers to B, and B wins.

But then, 15 other people whose sincere preference is CBA
decide to do their civic duty, and take the trouble to show up
& vote, in the hopes that they might improve the outcome for
themselves and those whom they care about:

40: ABC
25: B
35: CBA


Now, C eliminates B, and then C loses to A, and A wins.

(If anyone objects to B voters not listing a 2nd choice, B
is middle, and it's reasonable to assume that their 2nd choice
votes would go both ways, if B voters even have a preference
between A & C. In any case, the example works even if B's
2nd choice transfers aren't exactly equal in both directions.
I didn't list B voters' 2nd choices because I wanted to simplify).


They should have stayed home if they were going to vote
sincerely in IRV.


By the way, it's obvious that if C were someone's 2nd choice,
and their 1st choice were some D who was going to immediately
get eliminated, it would be a big mistake for a D voter to
list a 2nd choice in that election. If he did, then he makes
A win. If he truncates, voting only for D, then B wins.

So the IRVies' claim that IRV doesn't give incentive to truncate
isn't true, just as IRV also gives people good reason to
stay home rather than show up & vote sincerely.


Mike Ossipoff

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