[EM] Irrelevant Ballots Independent Fallback Approval (IBIFA)

[fsimmons at pcc.edu]

Chris,

I like this method.  It accomplishes more simply what I was trying to do with some of my DSV approval 
methods:

Voters can approve good candidates with less risk for regret, because if their lower approvals wreck an 
approval victory of their favorite, the IBIFA method detects this state and compensates for it.

Both the three slot and four slot versions seem like definite improvements over both Approval and Bucklin 
without sacrificing the FBC, definitely worth testing and examining in more depth.

Forest


----- Original Message -----
From: Chris Benham 
Date: Wednesday, June 16, 2010 10:27 am
Subject: Irrelevant Ballots Independent Fallback Approval (IBIFA)
To: EM 
Cc: Kevin Venzke 

>  "Irrelevant Ballots Independent Fallback Approval" (IBIFA) is 
> the name I've settled on for the method I proposed
> in a May 2010 EM post titled "Bucklin-like method meeting 
> Favorite Betrayal and Irrelevant Ballots".
> 
> http://lists.electorama.com/pipermail/election-methods-
> electorama.com/2010-May/026479.html
> 
> In that post I wrote that it uses multi-slot ratings ballots, 
> and defined the 4-slot version:
> 
> 
> *Voters fill out 4-slot ratings ballots, rating each candidate 
> as either Top, Middle1, Middle2
> >or Bottom. Default rating is Bottom, signifying least preferred 
> and unapproved.
> >
> >
> >Any rating above Bottom is interpreted as Approval.
> >
> >
> >If any candidate/s X has a Top-Ratings score that is higher 
> than any other candidate's approval
> >score on ballots that don't top-rate X, elect the X with the 
> highest TR score.
> >
> >
> >Otherwise, if any candidate/s X has a Top+Middle1 score that is 
> higher than any other candidate's
> >approval score on ballots that don't give X a Top or Middle1 
> rating, elect the X with the highest
> >Top+Middle1 score.
> >
> >
> >Otherwise, elect the candidate with the highest Approval 
> score.*(Obviously other slot names are possible, such as 3 2 1 0 
> or  A B C D or  Top, High Middle, Low Middle, Bottom.)
> 
> The 3-slot version:
> 
> 
> *Voters fill out 3-slot ratings ballots, rating each candidate 
> as either Top, Middle
> >or Bottom. Default rating is Bottom, signifying least preferred 
> and unapproved.
> >
> >Any rating above Bottom is interpreted as Approval.
> >
> >If any candidate/s X has a Top-Ratings score that is higher 
> than any other candidate's approval
> >score on ballots that don't top-rate X, elect the X with the 
> highest TR score.
> >
> >Otherwise, elect the candidate with the highest Approval score.*
> >
> 
> It can also be adapted for use with ranked ballots:
> 
> 
> *Voters rank the candidates, beginning with those they most 
> prefer. Equal-ranking and truncation
> are allowed.
> 
> Ranking above at least one other candidate is interpreted as Approval.
> 
> The ballots are interpreted as multi-slot ratings ballots thus:
> An approved candidate ranked below zero other candidates is 
> interpreted as Top-Rated.
> An approved candidate ranked below one other candidate is 
> interpreted as being in the second-highest
> ratings slot.
> An approved candidate ranked below two other candidates is 
> interpreted as being in the third-highest
> ratings slot (even if this means the second-highest ratings slot 
> is left empty).
> An approved candidate ranked below three other candidates is 
> interpreted as being in the fourth-highest
> ratings slot (even if this means that a higher ratings slot is 
> left empty).
> 
> And so on.
> 
> 
> Say we label these ratings slot from the top A B C D etc. 
> A candidate X's A score is the number of ballots on which it is 
> A rated. 
> A candidate X's A+B score is the number of ballots on which it 
> is rated A or B.
> A candidate X's A+B+C score is the number of ballots on which it 
> is rated A or B or C.
> And so on.
> 
> 
> If any candidate X has an A score that is greater than any 
> other candidate's approval score on ballots
> that don't A-rate X, then elect the X with the greatest A score.
> 
> Otherwise, if any candidate X has an A+B score that is greater 
> than any other candidate's approval score
> on ballots that don't A-rate of B-rate X, then elect the X with 
> the greatest A+B score.
> 
> And so on as in the versions that use a fixed number of ratings 
> slots, if necessary electing the most
> approved candidate.*
> 
> This is analogous with ER-Bucklin(whole) on ranked ballots:
> http://wiki.electorama.com/wiki/ER-Bucklin
> 
> 
> 
> 
> 
> Chris Benham
> 
> 
> 
> 
>