[EM] Re: ICC and Approval

[James Green-Armytage]

James replying to Mike, on the subject of ICC definitions...

James:
>So, ICC definition is changed to this, for use in evaluating non-ranked
>methods:
Mike:
>I trust that you meant "in evaluating both rank and non-rank methods".
>The 
>kind of ICC that you describe applies meaningfully and usefully to rank 
>methods and non-rank methods. To all methods.
>I trust that you wouldn't use different ICC definitions, one for rank 
>methods and one for non-rank methods.

	Yes, but if we apply the universally applicable (preference) version of a
criterion to rank methods (that allow equal ranking), it becomes
equivalent to the corresponding votes only criterion, and hence the extra
verbiage is unnecessary.

>Set S is a clone set if, for every particular voter, and for any
>candidate X 
>outside S,  if that voter prefers somone in S to X than s/he prefers 
>everyone in S to X; and if that voter prefers X to someone in S, then
>s/he 
>prefers X to everyone in S; and if that voter is indifferent between X
>and 
>some candidate in S, then s/he is indifferent between X and every
>candidate 
>in S.
>A voter is indifferent between X and Y if s/he doesn't prefer X to Y and 
>doesn't prefer Y to X.
>[end of clone-set definition]

	Sounds good to me.
>
Mike:
>You left out the stipulation about how preference constrains voting. The 
>usual one for ICC is that everyone votes sincerely.

	Right.
>
James:
>	I have proposed a modified version of ICC such that candidates must be
>given identical cardinal/approval scores by all voters to qualify as
>clones, in addition to the standard qualification rule. I believe that
>approval and cardinal pairwise both pass this modified version of ICC, but
>not the standard ranked ballot version.
Mike:
>No criterion should have a special ranked-ballot version. The ICC that
>you 
>described, or my improved wording of it, is ICC for all methods.

	Yes. For that reason, the criterion I suggest should be considered to be
a separate criterion from traditional ICC.
>
>By your alternative clone-set definition, there can be no such thing as a 
>clone-set with more than one candidate when the method is Plurality, or
>when 
>the method is Borda or IRV, as those latter two are usually propoed. 

	I should clarify my proposed criterion by saying that the additional
requirement only applies if the method has a cardinal ballot. In that
case, plurality and Borda continue to fail, while IRV continues to pass.

>One could write a preference clone set definition that says that S is a 
>clone set if everyone is indifferent between S's members. Pluralty,
>Borda, 
>and IRV would fail the resulting criterion, meaningfully. But you
>shouldn't 
>call it a clone set, because that name is already taken. How about 
>"indifference set"?

	Okay, but are you sure that IRV fails?
>

Sincerely,
James