[EM] IRV in San Francisco

Eric Gorr eric at ericgorr.net
Mon Nov 15 08:38:58 PST 2004

At 8:16 PM -0800 11/14/04, Bart Ingles wrote:
>Eric Gorr wrote:
>>At 7:44 AM -0800 11/12/04, Justin Sampson wrote:
>>>On Fri, 12 Nov 2004, Eric Gorr wrote:
>>>  > Well, it will cause IRV to fail the Independence of Clones Criterion and
>>>>  thereby be subject to a spoiler effect again.
>>>Doesn't IRV suffer from spoiler effects anyway?
>>The method itself passes the ICC, so spoilers cannot come from there.
>Take a hypothetical IRV variant where candidates are eliminated at 
>random, until a "majority" winner emerges.  Would this method still 
>pass ICC?

I cannot think of a case where random elimination of a candidate tied 
for least votes would cause IRV to fail ICC.

The only tie-breaker that I can think of in common usage (it gets 
written in to proposed laws) which would cause the implementation of 
IRV to fail ICC would be what I have called "deterministic"...where 
all candidates tied for least votes are eliminated at the same time. 
With this tie breaker, if the clones have > 50% support from the 
voters, it is possible to develop a case where they split the vote 
between them equally and are are eliminated causing a clear minority 
candidate to win the election.

>If so, is the method spoiler free?

Depends on whether one wants to consider spoilers in the context of IIA.

There is always the possibility that spoilers can come from 
directions other then ICC and IIA.

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