Bayesian Investor Blog

Here are a few comments from Friday’s Prediction Markets Summit.
Chris Hibbert described a way that a market with multiple outcomes (such as for supreme court nominees, which list contracts for a number of people, plus one for the rest of the field) could improve liquidity with a modest software change. The system could generate bids and asks for a given contract by aggregating the opposite side of all the other contracts in that market, and generate a synthetic order which would sometimes be within the bid/ask range of regular orders.
Google’s Bo Cowgill reported that one legal problem that Google faces in implementing internal prediction markets is that they might sometimes spread information around the company that might make the people with that information insiders in a way that would complicate those employees’ ability to trade in Google stock. It sounds like the insider trading laws are onerous enough to create a nontrivial barrier to spreading information.
Newsfutures’ Emile Servan-Schreiber said that Newsfutures was supporting the use of internal corporate markets for some fairly big corporate decisions.
Mike Knesevitch of Intrade / Tradesports seems to have lots of experience in traditional financial markets. He said a good deal about the liquidity and accuracy of his exchange’s political markets. The Howard Dean contract went from 33 to 9 within about 5 minutes following Dean’s “implosion” speech. Part of Tradesports’ reluctance to make it’s prices easy to link to is the possibility that they will charge money for those prices much like traditional stock and futures exchanges do. I wish there were a good way for users to persuade new exchanges to commit to keeping information free, but I don’t see a practical way to do that.
HedgeStreet’s Russell Andersson reported that CFTC approval for new contracts was easier than I expected. It takes about 24 hours for contracts dealing with things that the CFTC normally deals with, but weeks to months for other topics. (Why so much variation??)
Microsoft Todd Proebsting is surprisingly enthusiastic about most (all?) of Robin Hanson’s vision of what prediction markets might do. He reported a case where a market did a much better job of predicting when a product would ship than the manager did, although there was some confusion when the market fluctuated when it’s prediction created some uncertainty over whether features would be cut to make the deadline (the contract didn’t adequately specify how it would be judged if the product changed significantly). He reported that there was no resistance to prediction markets from upper management (middle management resisted, since the markets are designed to indicate failings of middle management). He mentioned that laws regulating sweepstakes created some obstacles to implementing internal corporate markets (they’re designed to prevent a sweepstakes game from rewarding the people who control the sweepstakes). He inadvertently(?) promoted the use of open source licenses by mentioning that legal concerns deterred him from looking at Robin’s market scoring Lisp code, which has no license granting any permission to use it.
Eric Zitzewitz responded to Manski’s theoretical criticisms of prediction market accuracy (see his paper on Interpreting Prediction Market Prices as Probabilities), and described some problems with inferring causality from markets and how to structure markets to minimize those problems (see his paper on Five Open Questions About Prediction Markets). He showed an amusing graph indicating that Tradesports prices implied Osama was twice as likely to be captured in October 2004 as in November 2004 (implying some connection with the U.S. elections).