[EM] Smith IBIFA

C.Benham cbenham at adam.com.au
Fri Jun 14 11:03:46 PDT 2019

IBIFA very naturally meets Plurality, Minimal Defense and Non-Drastic 
Defense so it occurred to
me to use it as a "Condorcet-completion" method thus:

*Voters fill out out either unlimited rankings ballots or multi-slot 
ratings ballots.

A  pairwise-beats-all candidate wins. Otherwise carry on the IBIFA 
process until a
Smith-set member qualifies. If only one does that candidate is elected.

If more than one does in the same round, then simplest and probably good 
is just to elect the one with highest score in that round.*

(That last provision is Bucklin-like as in original IBIFA. Using the 
Smith set the more
complex Relevant Ratings and the possibly a bit arbitrary-looking 
"revised IBIFA"
I think would be very unlikely to give  different winners.)

I think this is my favourite method that meets both Condorcet and 
Minimal Defense.

Also it can be used with an approval cutoff  to meet what Forest was 
asking for on 30 May 2019.

All rankings/ratings would be used to identify the Smith set, but for 
the IBIFA stage ballots would
be treated as if they truncate all their unapproved candidates. The 
default should be approval of
all candidates voted above at least one candidate.

Chris Benham

*Forest Simmons* fsimmons at pcc.edu 
/Thu May 30 /

> In the example profiles below 100 = P+Q+R, and  50>P>Q>R>0.
> I am interested in simple methods that always ...
> (1) elect candidate A given the following profile:
> P: A
> Q: B>>C
> R: C,
> and
> (2) elect candidate C given
> P: A
> Q: B>C>>
> R: C,
> and
> (3) elect candidate B given
> P: A
> Q: B>>C  (or B>C)
> R: C>>B. (or C>B)

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