[EM] Re: Later-no-harm, "Earlier-no-harm"

[Kevin Venzke]

Chris,

 --- Chris Benham <chrisbenham at bigpond.com> a écrit :
> "Mono-add-top" is a Woodall criterion which says that adding ballots that all give
> first-preference to X must not harm X. It is met by IRV and Margins, but not by WV.

How did you find that Margins meets Mono-add-top?  I have a hard time 
believing that.


 --- Chris Benham <chrisbenham at bigpond.com> a écrit : 
> On  Tue.Dec.23, 2003,  Kevin Venzke wrote:
> 
> "It's possible to define (a possibly limited version of) later-no-harm
> as: "Adding strict preferences among candidates otherwise ranked last,
> should not hurt the result of the election from the perspective of
> this ballot."
> 
> (By this definition, however, Approval passes, since approving an
> additional candidate doesn't just involve adding strict preferences,
> but also deleting others.)"
> 
> Surely Later-no-harm is only applicable to ranked-ballot methods,and Approval
> is not a ranked-ballot method. 

According to Woodall, Approval fails Later-no-harm.

> Other than trying to provide some ammunition for Approval versus IRV propaganda, 
> is there any point to this new version?

On the contrary, I recognize it as a limitation that Approval passes
my definition.  I came up with it because it is simple, and because
it could be reversed to illustrate "earlier-no-harm."

> 
> On a posititive note, Kevin went on:
> "I don't believe I've ever heard anyone suggest the obvious counterpart,
> "earlier-no-harm:" "Adding strict preferences among candidates otherwise
> ranked FIRST, (etc...)."
> 
> For example, if voting "A=B=C>D>E" gets me one of those first choices,
> then voting "A>B>C>D>E" should not get D or E elected.
> 
> "Earlier-no-help" could also be defined.  If "A=B=C>D>E" elects D,
> then "A>B>C>D>E" should not elect A."
> 
> I very much like the substance of this. On Mon.Dec.1,2003, I wrote:
> "I think that it is absurd that half an even number of voters voting AB and the other 
> half BA should have a different effect from all of them voting A=B, and also that it is 
> unfair that a faction of voters who  support candidates A and B by all voting either 
> AB or BA, should be in any way disadvantaged compared to a faction who support candidates 
> C and D by all voting C=D."
> The part after "and also.." I see as being equivalent to your "earlier-no-harm". I think 
> I would sum up the idea behind your 2 "earlier-no-h..." criteria in a "Decisiveness Fairness
> Standard" which says something like 
> "a faction of voters who all vote a set of candidates over all other candidates should not be 
> advantaged or disadvantaged by voting equal preferences (versus not)".
> Have I been wrong to assume this is connected with Symetric Completion/fractional equal
> preferences?

If you're right, it's not because I thought it was.

Woodall groups SC, LNHarm, and LNHelp together, and that's the main reason
I have to suspect that there's a connection.

I think you're supposing that LNHarm with LNHelp together imply SC.  I
can't find anything to disprove that.  So I suppose ENHarm plus ENHelp
might imply a reversed kind of SC.

The point of "earlier-no-harm" is to remove the incentive to compromise by
upranking everyone to first.  That would remove the possibility of multiple
candidates being majority favorites unless the voters really felt that
way (or they didn't understand the method's features).

SC applied to candidates that the voter tied in first would not be
nearly as repugnant to me as SC applied to candidates that the voter
didn't rank at all.

> Can a method meet Earlier-no-harm/help without complying with SC?

I'm almost positive of that, since methods can meet LNHarm/help without
meeting SC.  I don't see a big difference between the two pairs.

I'll devise a method which meets Earlier-no-harm for the next time I post.
I doubt it will meet Majority, though.


Kevin Venzke
stepjak at yahoo.fr


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