[EM] No evidence that IRV doesn't fail. Reasons why it must.

Eric Gorr eric at ericgorr.net
Fri Jan 23 13:19:06 PST 2004

At 2:43 PM -0600 1/23/04, Paul Kislanko wrote:
>??? You said the same thing I did, but didn't recognize that's what you did.
>>>Eric wrote:
>>>>Consider the case of a polarizing issue, such as Abortion. To
>>>>those on either side, their last place vote will matter just as
>>>>much as their first place vote. Even their middle preferences
>>>   >will matter greatly as it puts a buffer between the viewpoint
>>>>they agree with and the viewpoint the simply hate.
>>>There are a lot of implicit assumptions here about which voting method is
>>>being used. You are assuming that fully ranked ballots are being used
>>I have made no such assumption.
>You make the same assumptions in this reply below.
>>Pretend that Candidate A is pro-abortion. Candidate N is
>>anti-abortion. The voter could easily rank:
>>    A > B = ... = M > N
>>If the voter sees no relative difference of candidates B - M, there
>>is no need to fully rank them.
>Exactly. So there's no reason to assume N is more "disliked" than M.

There is no need to assume.
N _IS_ more disliked then M.

If this were not the case, the voter might simply vote:


or, equivalently,

   A > B = ... = N

or, ....

>In your original post you didn't allow "=",

Yes, it did.

>your example of a polarizing issue would suggest
>    A=B=C...>... X=Y=Z
>and in your original post you suggested that that Z could be considered
>"most disliked" in a ranked-ballot method,

I suggested no such thing.

>  but with equal rankings allowed your original suggestion is untenable.

I would simply say that all the alternatives on the right hand side 
of the '>' are "most disliked". That there is more then one which can 
be labeled with "most disliked", is obviously irrelevant.

However, even within a polarizing issue, it is entirely possible that 
a voter would do:

   A > B = ... = Y > Z

which would imply that B - Y all felt the same way as A with respect 
to this issue, but the voter believes there to be a merit difference 
between A and B-Y - what that different might be is irrelevant. 
However, since Z does not believe the same as A, the voter again 
finds a merit difference between A & B-Y.

We are still dealing with the case of a polarizing issue.
All rankings do matter.

IRV assumes that all rankings don't matter.

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