Hayekian Prediction Markets?
I think I basically get the idea behind prediction markets. People take their money seriously, so the opinions of people who are confident enough to bet real money on those opinions deserve to be taken seriously as well. That kid on the schoolyard who was always saying "wanna bet?" might have been annoying but he also had a point: your willingness or unwillingness to bet does say something about how seriously your opinions ought to be taken. Furthermore, there are serious problems with the main alternative prediction method, which consists of asking experts what they think is going to happen. Almost nobody ever keeps track of whose predictions turned out to be right and then listens to those people more. Some predictions involve events that are so rare or so far in the future that there's no way for an expert to accumulate a track record at all. Some issues give experts incentives to be impressively wrong rather than boringly right. And so on. These are all good points, and they make enough sense to me to convince me that prediction markets deserve to be taken seriously and tested empirically. If they reliably produce better predictions than the alternatives, then they deserve to win the day.*
But there is a particular claim that is made about prediction markets that I am skeptical of. It starts with the well-known idea, usually associated with Friedrich on Hayek, that a major virtue of free markets is that there is all kinds of useful information spread out in local chunks throughout the economy, which individuals can usefully exploit but a central planner never could, which is reflected in market prices, and which in turn cause resources to be allocated efficiently. It then goes on to argue that prediction markets have a similar virtue. As an example, suppose there's a prediction market for a national election, and you happen to know that Candidate X is more popular in your little town than most people think. There's no way that some faraway expert could have known this or incorporated it into his or her prediction in any way, but it gives you an incentive to bet on Candidate X, which causes your local information to be reflected in the prediction market price. Lots and lots of people doing the same thing will cause lots and lots of such little local pieces of information, which couldn't have been obtained any other way, to also be reflected in the market price.
But it seems to me that this "Hayekian" mechanism should work a lot less well in the prediction market context than in the standard context. In the standard version, you benefit directly from a piece of local information that only you happen to have. If you know that a particular machine in your factory only works right if you kick it three times on the left side and then smack it twice on the top, then you can do that and directly reap the benefits, and the fact that you were able to do it (i.e., the fact that output in your particular industry is very slightly less scarce than someone who didn't know that trick would have thought) will be reflected in the market price. In contrast if you're the only one who knows that Candidate X is surprisingly popular in your little town (say because you're the mail carrier and you count yard signs along your route), could you really benefit from trading on that information? There are a number of barriers to your doing so. First, there are transactions costs associated with trading. Second, there is garden-variety risk aversion: if you're risk-averse then you won't want to invest a large share of your total wealth in this highly risky and urnhedged asset, which means that you won't bet much and so the price won't move much to reflect your information. Third, in order to believe that your little piece of local information constitutes a reason to bet on Candidate X, you'd have to believe that the current price accurately reflects all the *other* pieces of information besides yours. In some sense you should believe this: if you thought the price was off and you thought you knew which direction it was off, that would be a good reason to bet against the mispricing. But even if you had no actionable beliefs regarding a mispricing, you might just not have a lot of confidence that all the other information has been aggregated correctly. This would translate into another form of risk, and so risk-aversion would kick in once again. Fourth, there may be uncertainly about whether you really are the only one who knows knows your piece of local information (maybe the paper boy also noticed the yard signs, but then again maybe not). If you're not sure, then you're not sure to what extent that piece of information is already reflected in the current price. Again, you might have beliefs about this, and those beliefs might be right on average (though they might not) but it is yet another layer of uncertainty that should have an effect similar to ordinary risk aversion.
I asked Robin Hanson about this once at lunch a few years ago, and we had an interesting chat about it, along with some other George Mason folks. I won't try to summarize everyone's positions here (I'd feel obligated to ask their permission before I'd even try), but suffice it to say that I don't think he foreswore the Hayekian idea entirely as an argument in favor of prediction markets. And there is a quote by him here that seems to embrace it. In any case, I'd be interested to know what he thinks about it. And of course it matters whether or not this Hayekian claim is being made for prediction markets, and it matters whether the claim is correct, because whether or not prediction markets have this additional theoretical advantage should go into one's priors about their merits before evaluating whatever empirical evidence becomes available.
*The question is not purely an empirical one though. There are issues related to how susceptible prediction markets are to manipulation, how well they'll work when the people doing the betting about what will happen also have some influence over what does happen, whether they'll work for rare or distant events, or for big picture questions where in some states of the world there's no one around to pay out the winnings, and so on. So even a strong empirical finding that prediction markets work in more straightforward settings is not the last word on the subject, which means that there will be a continuing role for theoretical arguments even as more evidence comes in.
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Comments (79)
Interesting: 40 comments, only 4 of which are visible by default...
*Not counting this one.
Politics is the mindkiller. The community sees it as damage and routes attention around it...
I think you missed.
I'm not sure there is a clear enough claim here to agree or disagree with. Pretty much all institutions aggregate information in some way, and this includes all sorts of markets. This aggregation can include not just directly reflecting info contributed by participants, but also informing participants, who then combine that new info with their old info, and then contribute that new combined info. Certainly there are barriers to such aggregation, which include transaction costs and risk aversion. The important question is of course the relative ability of different institutions to achieve this function; barriers exist in all institutions. Existing speculative markets seem to do a good job of this, and new design variations (e.g., combo markets) may do even better.
In the absence of decisive empirical evidence, the amount of credence to give to a particular prediction method (whether absolutely or relative to alternative methods) depends in part on what theoretical claims are being made for it, and on how well-supported those claims are. The articles that I linked to don't just say that prediction markets do reasonbly well in aggregating information, or that they do better than the alternatives. Rather, they make explicit reference to Hayek's famous argument which, as I understand it, involves a strong claim of incorporating lots of tiny pieces of information held locally by individuals. And without leaning too hard on a single quote, one of those articles seems to have you agreeing:
I think there is a fairly clear question here of just how strong an absolute "Hayeakian information aggregation" claim you are making.
A standard debating tactic is to attribute overly strong claims to the other side, which seem easy to knock down. You don't have any concrete quotes of such overly strong claims, so you seem to be just assuming someone must have said something overly-strong somewhere. Re the quote from me, that quote doesn't say how much info gets aggregated from any given group.
In the original post, I said regarding our sole conversation on the subject that I can reall:
Then I added:
That sentence had a link to an article that contained the quote in my comment above. Taken all together, does that really strike you as me "attibuting overly strong claims" to you? It sure doesn't strike me that way. I pointed out that you've said some things that seem to lean in a pretty "Hayekian" direction, explicitly acknowledged that I'm not certain to what extent you are making those kinds of claims on behalf of prediction markets (I'm still not), and asking you to clarify. If you think that's a debating tactic, then you and I have very different ideas of what a debating tactic is.
The debating tactic he seems to be referencing is that you seem to claim that large amounts of information will be added, while his claim is only that some information will be added ("don't think he forswore the Hayekian idea entirely" seems pretty weak). It also feels strongly like you are attacking the Hayekian idea, but not providing an attack; saying "I don't believe this" but not substantiating.
In case people are falling to representation bias from your example, here's a way the prediction market could work out:
One extremely ardent organizer or supporter from the town feels that with the amount of popularity she's experienced the candidate has a much better chance (perhaps due to selection bias from seeing the signs and speaking to reporters) than most predictors, she would see the prediction market as a better investment. And if the prediction markets were national in scope but more localized in specialized information (perhaps consider the recent Massachusetts senate race?), a local might have substantial reason to believe that they're local information would be better than national info.
I'm not as hot on the Hayekian principle as economists were, but I don't see how any of the factors you suggest would be different between a prediction market and a normal stock market.
And normal stock markets are pretty good at allocating ressources, up until the moments where everything goes berserk, so there's no reason to suspect that prediction markets would be much different.
The comparison in the post wasn't between prediction market prices and stock market prices, it was between prediction market prices and ordinary prices for goods and services. I hadn't thought about it before, but it seems to me that the points made in the post about prediction markets apply to stock markets as well.
Note that this isn't an argument that prediction markets (or normal stock markets) don't work. It's an argument about whether they have this particular "Hayekian" virtue.