[EM] Scott Ritchie's FAVS criterion - uniquely favors range voting

[Chris Benham]

Warren Smith wrote:

>About Scott Ritchie's "feel alike vote same FAVS" criterion
>that all members of a feel-alike group should want to vote the same.
>
>FAVS is falsified by IRV if incomplete information:
>  either A or B need 5 more votes to surpass the hated C and/or the 50% mark
>  (but you do not know which) and your group has 10 votes.  So split them.
>
>I am not sure whether FAVS is satisfied by IRV in complete information scenarios.
>
I don't know why you are not sure, because I pointed out in my last post 
that methods like IRV that are vulnerable
to Pushover strategy fail this "FAVS" criterion.

Suppose these are the known voting intentions:

48: A
27: B>A
25: C>B

On these votes, IRV eliminates C and elects B. The 48A supporters can do 
nothing to elect A if they all vote uniformly
(because if they give their first preference to A any second preferences 
won't be counted and obviously if they all give
their first preference to B or C then they will simply elect whichever 
one it is), but if  from 3 to 20 of them change their first
preference vote to C then B will be eliminated and elect A.

45: A
03: C>A  (or C, or C>B; sincere is A)
27: B>A
25: C>B

Apart from just offending mathematical elegance, this vulnerability to 
Pushover strategy is the reason why I care about
methods failing mono-raise.

Chris Benham


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