[EM] Scott Ritchie's FAVS criterion - uniquely favors range voting
Chris Benham
chrisjbenham at optusnet.com.au
Sat Dec 16 00:23:52 PST 2006
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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