[EM] Re: Voting Systems Study of the League of Women Voters of Minnesota
chrisbenham at bigpond.com
Wed Jun 8 08:42:03 PDT 2005
In response to Abdul asking:
>What if we had IRV with Approval? What is that called?
>Equal-Rank [allowed], Instant Runoff Voting, whole [votes counted for
>In other words, each round of the runoff becomes an approval election
>rather than a single-vote-transfer election.
This isn't the only method that qualifies "IRV with Approval". As I've
explained in previous posts, ER-IRV(whole) is much more vulnerable than
plain IRV to voters taking advantage
of its mono-raise failure with a Pushover-like strategy.
>> 45:Right=Left>CentreRight (sincere is Right>CentreRight)
>> First-preference tallies
>> Right:45 CentreRight:35 Left:65
>> CentreRight has the lowest tally, and so is eliminated then Right wins.
>> This time no coordination was needed. As long as the Right suporters
>> knew that Right had more first-prefernces than CentreRight, and a
>> pairwise win against Left, then each individual Right supporter got
>> an increased expectation by insincerely upranking Left from last to
>> equal-first with no risk.
> This would also work if the numbers 45/35/20 were replaced with 49/48/3.
For this reason I rate ER-IRV(whole) as worse than plain IRV.
A much better version of "IRV with Approval" is Approval Elimination
Runoff which fixes the elimination schedule by the initial approval
scores and has a majority stopping rule.
So if the candidate who is highest ranked (among remaining candidates)
on the most ballots is so on a majority of the (non-exhausted) ballots,
then that candidate wins. If not,
eliminate the (remaining) candidate with the lowest approval-score, and
The version that uses plain rankings ballots and interprets all ranked
candidates as approved (not allowing them to enter an explicit approval
cutoff and rank disapproved candidates)
is Woodall's Approval Alternative Vote (ApAV).
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