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Thursday, December 10, 2009

An Instant Runoff Voting Majority is not what you think

One of the claims in favor of instant runoff voting is that it provides a majority winner. That is true only if you redefine what "majority winner" means.

In San Francisco,"majority" is of the "continuing" ballots, not a majority of all ballots:

"If no candidate receives a majority of votes from the continuing ballots after a candidate has been eliminated and his or her votes have been transferred to the next-ranked candidate, the continuing candidate with the fewest votes from the continuing ballots shall be eliminated. All votes cast for that candidate shall be transferred to the next-ranked continuing candidate on each voter's ballot. This process of eliminating candidates and transferring their votes to the next-ranked continuing candidates shall be repeated until a candidate receives a majority of the votes from the continuing ballots." SEC. 13.102. - INSTANT RUNOFF ELECTIONS.(D) go to this link and type in the SEC. 13.102 in search box. Amended in March 2002.

In other words, the majority consists of the votes left after others are eliminated. The elimination of ballots and the exhaustion of ballots (the point a ballot does not have choices marked) is part of the reason that in many instant runoff voting elections often suffer majority failure.

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4 comments:

Psion said...

Majority failure occurs when the candidate preferred by the majority of voters doesn't win.

Choosing not to vote indicates the non-voter does not have a preference, or their preference is minimal enough not to warrant the time cost.

In a (non-instant) runoff election, you wouldn't claim majority failure because voters from the first round chose not to vote in the second round. They are simply indicating that they have no measurable preference among the remaining candidates.

Why should IRV be treated any different?

Dale Sheldon said...

"Majority failure occurs when the candidate preferred by the majority of voters doesn't win."

Yes. And this happens under IRV, most recently/notably in the Burlington VT mayoral election: Montrol was eliminated, and then Kiss won, even though a majority of voters preferred Montrol over Kiss (4,067 to 3,477). In fact pairwise, Montrol was preferred over every single other candidate.

http://rangevoting.org/Burlington.html

IRVs majoritarian failures are well known, but in this story, Joyce is reminding us that, in addition, the false-majorities IRV uses also ignore exhausted ballots. But that's just bitter icing on top of the sour cake of IRV.

Psion said...

The Burlington example shows a Condorcet criterion failure, not a majority failure.

Range Voting, on the other hand, can cause a majority failure:

http://en.wikipedia.org/wiki/Majority_criterion#Range_voting

However, this is off the point of my original comment. I was making the point that exhaustion of ballots is not a bad thing (contrary to what the original post states). It merely indicates the voter does not have a preference among the remaining candidates.

Aggie said...

The person who refuted the Burlington race... I checked out the websites you listed and frankly, it doesn't make any sense. There's no way Montrol was the hands down winner. This system may not be perfect. I'm sure the Wright people weren't happy as in the first round, they had the majority but IRV allows EVERYBODY'S vote to count. This is democracy. It's a hell of a lot better than what we have. And if takes a bit more time and effort, it should! This is important stuff.