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Is InTrade being manipulated? Why does InTrade give a discounted probability for Barack Obama as US president?

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A quick link panorama.

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#1. Is InTrade being manipulated?

– Nate Silver shows that there are abrupt downward pressures on the Barack Obama event derivative, while we also see some abrupt upward pressures on the Hillary Clinton event derivative.

However, you can see by yourself that InTrade is resilient enough and does a great job of going back to normal [*], after just a few hours of trading:

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– At Portfolio, blogger Zubin Jelveh blows the incidents out of proportion.

– Professor Lance Fortnow has a more careful analysis and notes that the price of the Barack Obama bounces back quickly enough.

– Quick thought: Maybe the media should use an average of event derivate prices for the last 5 work days&#8230- so that the abrupt perturbations would be eliminated.

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[*] UPDATE:

Professor Eric Zitzewitz:

I’m not sure you can conclude from Silver’s graphs that the market goes “back to normal.” You can conclude that it moves back in the opposite direction of the impact those large trades. Back when the Hillary for President market looked like it was being manipulated, it appeared that the manipulator was both placing a large purchase and then placing limit orders to provide price support and slow down the reversion of the price.

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UPDATE: Are we witnessing manipulation attempts on the &#8220-Florida to vote Republican&#8221- prediction market at InTrade?

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#2. Why does InTrade give a discounted probability for Barack Obama as US president?

– As you remember, Emile Servan-Schreiber of NewsFutures believes that it&#8217-s a Republican conspiracy all over.

– Professor Justin Wolfers puts up an hypothesis: it&#8217-s legally impossible for US traders to arbitrage on BetFair.

– InTrade put up a crappy excuse: the industry is still too &#8220-young&#8221-. How lame. How stupid. The industry was younger in the previous elections, where arbitrage opportunities didn&#8217-t exist according to professors Justin Wolfers and Eric Zitzewitz (see their 2004 paper and their other publications).

– Blogger Zubin Jelveh swallows the InTrade P.R. line, and adds another crappy InTrade P.R. line: More arbitrage opportunities are being exposed in open air because much more observers are hunting down arbitrage opportunities in 2008 than in previous elections. That&#8217-s a second blatant cretinery, uncorrected by the Portfolio blogger. Re-read Justin Wolfers&#8217- blog post. Professor Justin Wolfers states that:

The current variation in price is larger than I have ever seen in my years of studying prediction markets. The forces of arbitrage that would typically eliminate these differences have been handicapped by the legal restrictions preventing U.S.-based traders from using overseas markets.

– Finally, professor Lance Fortnow says nothing about the arbitrage opportunities between InTrade and BetFair, but does offer some technical points about the issue of polls versus the prediction markets, centered around the question of state correlations. Read on.

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UPDATE: Eric Crampton (a Canadian exiled in New Zealand) says he has managed to turn a buck by arbitraging between InTrade and iPredict New Zealand. He also makes 2 theoretical points. Go read it.

UPDATE: Greg Mankiw just linked to Nate Silver.

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Simulating joint dynamics of InTrades electoral prediction markets

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from: Cody Stumpo
subject: Simulating joint dynamics of InTrade&#8217-s electoral prediction markets
mailed-by: gmail.com

Hi there,

I am writing you as experts on prediction markets to ask what you think of some work I have done. At InTrade, you can bet on the 51 electoral markets individually. So using these 51 time series, I generated a daily return covariance matrix to simulate the joint dynamics of how they might move forward in the days until the election. Assuming a normal copula of daily returns and simulating the 48 (IIRC) days until the election 5000 times, I get a distribution of outcomes. The histogram of Obama electoral votes (which interestingly is bimodal) is the main output. The mean is 259 – and the chance he will win the election (as of yesterday&#8217-s close) was 44.4%. This agreed almost exactly with http://www.fivethirtyeight.com which is the best polls-based approach I know of.

Some more details are on my blog, http://houseofcramps.blogspot.com/ . You are free to use/extend the idea, with credit.

Regards,

Cody Stumpo

Nobel laureate Gary Becker and judge Richard Posner both wish that, one day, real-money prediction markets will be legal, without restrictions, in the United States of America.

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Via David Pennock of Odd Head fame

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Gary Becker:

[…] I believe that online political prediction markets, and other online prediction markets as well, should be legal in the United States and elsewhere, even if the amounts bet were quite large. There is no important substantive difference between such online betting markets and the Chicago Mercantile Exchange and other exchanges that allow individuals and organizations to take positions on movements of stock indexes, housing price indexes, and prices of other derivatives. A distinction is sometimes made between political betting markets and derivative markets since participants in derivative markets may be hedging other risks that they face. Yet this distinction has little substance since if larger bets were allowed in online political markets, groups whose welfare depended greatly on political outcomes would make greater use of these markets. For example, if a Republican presidential win would mean greater spending on military weapons, companies in the arms business might hedge their risks by betting on Barack Obama.

If large bets were allowed, some wealthy groups may bet a lot on their candidates in order to exert bandwagon influences on public opinion through their large bets affecting market odds. If so, these markets likely would become less reliable as predictors of outcomes, and hence would have less influence on opinions. To a large extent, therefore, these markets would be self correcting, although online political markets might place various other restrictions on bets, as is common in derivative and other exchanges.

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Richard Posner:

[…] There is an interesting question whether prediction markets should be thought of as &#8220-gambling” and perhaps prohibited. As a matter of policy, that would be a mistake, even if one thinks that gambling should be prohibited. The prediction markets are markets for speculation, rather than for game-playing or risk-taking. Slot machines, card-playing, roulette wheels, and other conventional forms of gambling do not generate socially valuable information. Speculation does. Commercial speculation serves to hedge commercial risks and bring prices into closer phase with value. Political, cultural, etc. prediction markets also yield socially valuable information. The outcome of elections is important to companies and even individuals for whom particular public policies are important- they may wish to make adjustments to avert or exploit looming political change. Politicians too need to have as sharp a sense as possible about the effects on the electorate of their and their opponents&#8217- strategies. Apparently they can get more accurate information from the prediction markets than from the public opinion pollsters.

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Do the top brass really tell everything to the trading employees? Do the EPM traders have access to all the primary indicators?

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Prediction markets: the future of decision-making – Companies are now making business decisions based on information employees provide via internal trading systems. – The Times of London – 2008-09-04

&#8220-We use them [“them” = the enterprise prediction markets] as another point in the decision-making process, alongside asking experts and other business leaders,&#8221- said Christina LaComb, a computer scientist in the R&amp-D lab at GE.

OK. You&#8217-re using enterprise prediction markets- you&#8217-ve gotten your name in the newspapers- you&#8217-re &#8220-cool&#8221-.

And our good friend David Perry&#8217-s gotten your money.

But do your event derivative traders have the same access as you do to &#8220-experts&#8221- and other &#8220-business leaders&#8221-?

Or do you leave them in the dark? In that case, your enterprise prediction markets would be clueless, useless, and worthless.

Nigel Eccles (the CEO of HubDub) and Robin Hanson (the inventor of MSR) have some explaining to make about the extreme zigzagging of the Barack Obama event derivative (in blue on this static compound chart). Look at the right end of the chart.

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UPDATE:

Nigel Eccles:

There was a bug in that chart which is now fixed. However the excess volatility is still there. The problem is that our early markets were created with a liquidity parameter which was too low. That is fixed with more recent markets. However we are also looking at modifying the MSR in some significant ways.

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Previously:

– the latest InTrade predictions

– Emile Servan-Schreiber&#8217-s post on market arbitrage

Is Intrade out on a limb?

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As I write this, Intrade gives the advantage to McCain over Obama and has the Republican party even with the Democratic party to win the election, whereas all the other prediction markets, meaning IEM, Betfair, and the NewsFutures play-money kind still favor a Democrat in the White House. That disconnect prompted Chris to wonder aloud whether Intrade is faster than the other markets to incorporate the latest polls, perhaps because of its &#8220-bigger liquidity&#8221-.

That&#8217-s an interesting reaction on several levels.

First, reactivity and accuracy are not to be confused for one another. Given that market prices are supposed to be more accurate and more stable that fickle U.S. raw polls (Berg et al, 2008), one should not necessarily be impressed by the market that is quickest to mirror the latest polls. I very much doubt that traders in the &#8220-other&#8221- markets have not heard about the latest polls giving McCain an edge. Rightly or wrongly – it is too soon to tell – they just gave those polls less weight that the Intrade traders apparently did.

Second, the argument from &#8220-bigger liquidity&#8221- is not receivable. Recently, Paul Tetlock analyzed Tradesports data in depth and found that more liquidity may in fact make the market dumber. He concludes: &#8220-In both sports and financial prediction markets, the calibration of prices to event probabilities does not improve with increases in liquidity- and the forecasting resolution of market prices actually worsens with increases in liquidity.&#8221-

My personal theory is that Intrade has a hair-trigger Republican bias which is not found in the other markets, because Intrade appeals to, and is marketed to, the more Republican-leaning segments of the U.S. population. In my opinion, the Intrade/Tradesports Republican bias was already evident in the 2004 election, as this analysis shows.

Of course, I may be completely wrong. In any case, I find today&#8217-s dual disconnect between the polls and most of the markets, on the one hand, and between Intrade and the other markets, on the other hand, to be two very interesting data points that should be duly recorded so we can come back to them later, with hindsight.

WORLDS #1 PREDICTION MARKET GURU DELIVERS THE SPEECH OF THE CENTURY, THEN LOSES HIS VOICE.

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Combinatorial Prediction Markets – by Robin Hanson

Video + Slides

Slides from Hanson&#8217-s site – PPT file

Folks, this is great stuff. I may blog about it, again, later on &#8212-if I find time.

You can blog about it on Midas Oracle, if you wish. Or comment on it, just below. Do register yourself.

2008 US ELECTORAL MAP PREDICTION: The 2008 US elections thru the prism of the prediction markets – 2008 US presidential and congressional elections – US President Prediction + US Congress Prediction – Barack Obama vs. John McCain

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#1. Explainer On Prediction Markets

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Prediction markets produce dynamic, objective probabilistic predictions on the outcomes of future events by aggregating disparate pieces of information that traders bring when they agree on prices. Prediction markets are meta forecasting tools that feed on the advanced indicators (i.e., the primary sources of information). Garbage in, garbage out&#8230- Intelligence in, intelligence out&#8230-

A prediction market is a market for a contract that yields payments based on the outcome of a partially uncertain future event, such as an election. A contract pays $100 only if candidate X wins the election, and $0 otherwise. When the market price of an X contract is $60, the prediction market believes that candidate X has a 60% chance of winning the election. The price of this event derivative can be interpreted as the objective probability of the future outcome (i.e., its most statistically accurate forecast). A 60% probability means that, in a series of events each with a 60% probability, then 6 times out of 10, the favored outcome will occur- and 4 times out of 10, the unfavored outcome will occur.

Each prediction exchange organizes its own set of real-money and/or play-money markets, using either a CDA or a MSR mechanism.

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More Info:

– The Best Resources On Prediction Markets = The Best External Web Links + The Best Midas Oracle Posts

– Prediction Market Science

– The Midas Oracle Explainers On Prediction Markets

– All The Midas Oracle Explainers On Prediction Markets

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#2. Probabilistic Predictions = Charts Of Prediction Markets

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Put your mouse on your selected chart, right-click, and open the link in another browser tab to get directed to the prediction market page of your favorite exchange.

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InTrade

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2008 US Electoral College

2008 Electoral Map Prediction = InTrade – Electoral College Prediction Markets = Probabilistic predictions for the 2008 US presidential elections based on market data from InTrade Ireland = electoralmarkets.com

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– This is a dynamic chart, which is up to date. Click on the image, and open the website in another browser tab to get the bigger version.

State Polls versus Electoral College Prediction Markets

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Prediction market analyst Lance Fortnow in an e-mail to me:

Right now the electoral college markets are tracking the polls pretty closely. I think we&#8217-ll see some divergence when we get close to the election since the polls can&#8217-t keep up. In past elections the markets were much better than the polls within a few days before the election (though not on election day itself which has too many rumors).

Other thoughts:
– There is a long-shot bias &#8212-states which are above 85% (for one candidate or the other) reflect a probability closer to 100%.
– The state markets are strongly correlated. There is a small but non-trivial chance that many states will be way off this year. And then people will be reluctant to trust the electoral college markets in the future.

So, I have (at least) one answer to my series of provocative questions: Electoral college prediction markets are more useful than the state polls towards the very end of the presidential campaign (but not on Election Day). Interesting. Thanks.

PS: The discussion about this post goes on in the comment area of another post.

Prediction Markets for the 2008 Electoral College = US Electoral Map

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Interesting blog post from Lance Fortnow on the VP prediction markets. (I will soon blog about those.)

InTrade – Electoral Markets Map

Their brand-new widget: