Saturday, February 18, 2012

IRV a Uniquely Poor Choice for Centrists

The other day, I noticed that the number-one referrer to this site recently has been Rise of the Center. So, first of all, thanks to them and everyone who's found their way here through them. Second, I have an important observation to share with you: instant runoff voting is a uniquely poor voting reform option for centrist. I was reminded of this fact while playing with Ka-Ping Yee's Voteline simulator, in order to respond to points made in the comments of my previous post on the Independence of Irrelevant Alternatives. And while it's something I've alluded too before, I don't think I've ever stated it this bluntly.

Model On Line

The Voteline simulator uses a very simple model. Voters are smoothly distributed along a left-to-right spectrum. Candidates occupy one point on that spectrum. Voter preferences are based on the linear distance from themselves to the candidates; closer candidates are preferred. The meanings of the colors may not be obvious though. The represent who the winner of the vote would be if the entire electorate were shifted, together, so that the median voter was at that point on the line. The relative distances between the candidates don't change, nor does the distribution of voters.

If you believe the winner of an election should be the candidate closest to the center of the political distribution, you would want an election method that always has a nice broad swath of matching color around each candidates' place in line, and 3 of the 5 methods used in Voteline do precisely that. The two that don't are plurality and "Hare (IRV)", AKA instant runoff voting. Instead, a candidate's place in line can easily be taken up with other colors, meaning that even if they are the most-centrist candidate, a different candidate would win the election.

It's not even that hard to squeeze a centrist candidate completely out of the running.

I've talked before about why we use models in these arguments. All models have their shortcomings though, and the one used here certainly contains some exaggerations; not all voters fall neatly on a single axis for instance (but see Yee's two-axis simulations) and we only have symmetrical voter distributions to play with here and so on. And there are other models in which IRV doesn't look quite as bad. But those models don't have any way of defining a center, so if you're buying into the idea of centrism, you don't have many other places to turn to for data.

It is certainly the case that voting method reform could help centrist. But, what these models suggest is that IRV is probably the least helpful voting method reform for that.


  1. Hey Dale. I can't remember if I've shared this with you before. But this video reinforces a lot of the issues that you mention using Ka-Ping Yee's simulator. You've got good stuff, as always.


  2. Thanks, Aaron. I remember when you shared your video with CRV (or was it CES?), but had forgotten about it! Although it'd be hard for me to claim it hadn't subconsciously inspired this post.

  3. This is, in fact, probably the strongest argumentagainst IRV, and one doesn't even need to go to models. The 2009 Burlington, Vt. mayorality election, in which plurality would have elected the rightist, and IRV actually elected the most extreme leftist, eliminating the most nearly centrist of the three, shows the point you make without resorting to models. IRV favors extremists. this is incontrovertible.

  4. True; I probably should have talked directly about Burlington, or at least linked to my posts about it:

    My initial story

    A reply to comments on that story

    Non-monotonicity in Burlington, Part I, and Part II

    And finally, a sarcastic response to Fairvote

  5. The Progressive candidate reelected in Burlington with IRV wasn't an extremist. He was the candidate for the top two party that was closest to the center in Burlington.

    When you let parties relocate around a dynamic center then IRV will incentivize for the two biggest parties to follow the center and together form a more dynamic de facto center. This is bad news for a "centrist party", but it's good news for "centrists" or those of us who want there to be more entanglement between the true center and the de facto center, without the latter completely tracking the chaotic path of the former.


  6. I would argue that the Democrat (Montroll) was closest to the center in that election. And I think that the fact that every single ranked-ballot method except irv agrees on Montroll as the winner (as well as approval and range with any half-reasonable assumptions about voter behavior), and the angry yet successful campaign to eliminate irv after this election, lends support to that argument.

    But true, describing Kiss (or Wright) as an "extremist" is perhaps a bit deceptive; I used the word as contrast against "centrist", not to paint them as members of some fringe group. Do you have a suggestion for a word that means "non-centrist" without being as clunky as "non-centrist"?

  7. non-Condorcet Winner(non-CW) is a possibility...

    IRV elected the non-CW because the GOP refused to move towards the center and its moderate voters didn't vote strategically when they refused to do so. With experience, this would have been fixed.

    And, it's arguably not the same thing: third-party dissenters being made to vote strategically, vs members of a major party that refuses to adapt being made to vote strategically. The latter bolsters the center, the former undermines it.

    The real issue is do we need a centrist party or do we need two major parties that must adapt to the dynamic political center?


  8. You're welcome for the traffic :)

    The point of election reform isn't to find the one that gives us the best outcome, it's the one that gives people the opportunity to cast their vote the way they'd like to.

    Personally I like the actual runoff, after a general election where nobody gets 50%+1, so people have one more chance to look at the two remaining choices one more time.

    I'd be happy to post data driven stuff like this on Rise of the Center, if you'd be open to that.


    Solomon Kleinsmith
    Rise of the Center

  9. I don't think letting them "cast their vote the way they'd like" is the best way to help voters. Voters manipulate their ballots because they want results. Give them better results, and they won't need to manipulate their ballots as much.

    But if all you really want is a ballot immune to strategic manipulation, regardless of the results, then there is a whole class of voting methods that can supply you with that. But I promise, you're not going to like it when you actually see it.

    But all snark aside:

    When I talk about outcomes, you can see that I measure it by decreased Bayesian regret. I think "decreased regret" is what YOU really want, too. But you don't get that through guaranteeing a strategy-free ballot. You get it by finding the best outcome the most often. (And usually, that means a more-centrist winner, too. Really, approval voting will help you! A lot!)


    I agree on runoffs, they're great! But again, that's because they (almost) always decrease regret. (Intriguingly, one of the rare exceptions is under score voting if most (>75%) voters are honest. But I have low expectations for voter honesty, which is why I'm happy with approval voting, which does still gain from a runoff, even with completely honest voters:

    And I would absolutely be open to data-driven stuff on RotC! I can provide you with all sorts of data, or if you're open to a guest post or two, I would be happy to supply that!

  10. The VPP aren't an "extremist" party, they're a centre left party, akin to the NDP in Canada or the various social democrat parties of Europe.

    And I'd argue, they've been a net benefit for the political environment in Vermont. But that's just me.

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  12. I don't know how anyone can call the NDP in Canada or a social-democratic party in Europe cent[er]-left. A party that openly advocats socialism is hardly "center" anything.

  13. They haven't been a socialist party for decades. You might want to look at their provincial administrations in British Columbia and Manitoba. The only reason they haven't dropped the symbolic gesture of "Socialism" is because Jack Layton asked it not be before he died. Expect it to be dropped sometime in the future.

    As for the Social Democratic parties of Europe, they're routinely designated "centre left". Labour, the SDP of Germany, PvdA of Netherlands, etc., are decisively centre left, especially compared to the solid/far left parties of Die Linke, and the like. In fact, Europeans would laugh at the notion of "Social Democrats" being "far left".

  14. "The VPP aren't an "extremist" party"

    True. I think I acquiesced to this fact in an earlier comment. They are however further from the (mythical?) center than the Democratic party, and I needed some word to draw the distinction. "Partisan" doesn't seem right, nor does "non-centrist".

    Any suggestions for a replacement word?