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If I own Yes shares am I allowed to purchase No shares to play a spread?

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I think this question does not make sense with the way the market works.

There are not separate markets for YES and NO; buying a YES is exactly the same as selling a NO you don't have, and putting up the collateral for delivery of the contract. If you were to buy a YES and then buy a NO, you would be in exactly the same position if you had bought a YES and then sold it, and you would have had the exact same impact on the market.

You cannot buy a spread between YES and NO, you can only buy a YES and then sell it later, or buy a NO and then sell it later.

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I wondered the same thing gary255. Can't tell if our inability to do that with the current software is a bug or a feature.  Maybe the folks designing the prediction market want a data-set of forecasts that aren't as complicated.  

Allowing us to take both side would have three benefits in terms of improving predictions:

(1) increases the availability of traders, essentially doubling our number, which should make it quicker for trades to clear.

(2) allowing us to forecast with more precision that just up/down. i.e. "the probability is above 25 but below 42"

(3) enabling the PredictIt market to to assemble a data set with dynamic predictions over time. As it stands now, once you forecast at a good price, no more info is collected about your assessment of the ongoing odds.

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Just to be clear, I'm not a Predictit rep.  I stumbled across this site when Bob Beckel mentioned it on afternoon television one day.

This site is very interesting.  But there are interesting limitations, including the number of shares of each prediction that are issued initially.  The concept of arbitrage seems to me to be contrary to what the site was intended to do -- measure the public perception of whether a political event would occur.  If someone is more interested in "making money" from the shares here than registering an opinion, it's not that hard to corner the market.  

I think the only way to prevent that is to limit the number of shares one may hold in a particular question, and a determined "investor" could likely circumvent that.

A lot of people owning a few shares will give better predictive results than a few holding large stakes attempting to double their money.  At least that's my perspective.  

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Well for example, there are two markets asking the exact same question: who will win the whitehouse in 2016. There's the "will the Dems win" market and the "will the reps win" market. A no in one is a yes in another. So you should be able to sell a "no the republicans won't win" to cancel out a position of "yes the democrats will win" otherwise the markets start being dumb. As it stands I can buy the same position in different markets and just hold them till the end and make a guaranteed profit (if I buy both side for less than 50 cents) that opportunity should not exist for longer than a split second in a functioning market.

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I would like to own both Yes and No shares in the same question - obviously at different prices in order to arbitrage the spread difference. 

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What you describe is not arbitrage, it's hedging.

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Candidly: Your answer 3 years ago still applies now, IMO, that PI is (allegedly!) for research purposes. People who want PI to mimic Stock Markets need to go play in them, if that is what they enjoy the most. Personally, I enjoy watching and learning the psychological factors involved in the fluctuations and resolutions of PI markets, by both the PI players and the public at large (Politicians, Constituents, Mass Media, etc) as much, if not more than the opportunity to make a buck or two profit here and there. re:"...The concept of arbitrage seems to me to be contrary to what the site was intended to do -- measure the public perception of whether a political event would occur. If someone is more interested in "making money" from the shares here than registering an opinion, it's not that hard to corner the market..."

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If the goal of this site is to produce price discovery - i.e. accurate/efficient market predictions - then Predictit should allow arbitrage. The combination of not allowing it and a confusing setup of separate YES and NO markets, is making for awfully large inefficiencies, which means the pundits won't be particularly interested. If the odds for all the Republican candidates adds up to 150%, for instance that obviously makes no sense. More money coming in will help, but so would the ability to arb, and so would a simpler system (a la the late Intrade).

As an aside, there are a number of posters who seem confused as to what constitutes arbitrage.


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Here's what I mean:

I don't think many people fully understand the NO markets. They come to the site and place money on YES bets they favor. Thus, YES prices are routinely inflated, something you can really see in multiple proposition markets like who will win the GOP nomination. If you add up all the probabilities, they routinely add up to way more than 100%, which obviously makes no sense. It's way better to bet NO in these markets.

So, let me amend what I said. It's not that NO markets are more inefficient. YES and NO markets are equally inefficient, it's just that the inefficiency tilts exclusively in one direction, i.e. NO.

This systematic bias isn't ideal for price discovery, something fans of prediction markets are keen on. Perhaps it's something that will sort itself out with more liquidity, but that shouldn't have to be the case. In the meantime, I will take solace in the trading opportunities that the inefficiencies provide.


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Candidly, I would agree that this is currently a small and therefore inefficient market. I find it fascinating and and interesting casual pastime. But why should that prevent the users from doing what I proposed? As long as the users understand the situation I don't see the harm.

Does a PredictIt representative respond to the forums? Or maybe Candidly is a PredictIt rep?

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What do you mean by saying that the NO markets are less efficient? YES and NO orders write to the same order book, and so they always have the same spread, and represent the same information...

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Blueraider, I'm not sure you follow what Gary means by "arbitrage," i.e., he wants to be able to buy and sell assets simultaneously to take advantage of market inefficiencies/differing prices. The Romney example you cite, assuming nobody is buying "yes," isn't applicable.

FWIW, I agree with most of the above comments. In fact, anything that would encourage more liquidity and smaller spreads, I think, should be welcome here.

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It seems more likely to me that the YES price inflation is due to the much lower dollar tie-up of buying YES shares in a multi-proposition market.

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The YES and NO markets are not actually separate though, so this question only applies to markets with multiple mutually exclusive options.

How did Intrade handle such cases?

I like the idea of only being able to own stock in YES or NO.  It means you have to actually be invested in your answer.  You make money on this site by buying the right stock (Whether it is stock you BELIEVE in or just something you believe will happen is personal choice), not by finding a profitable spread.

The only problem I see is if you have stock in one and then something that happens and you change your mind.  You can't buy any of the alternative stock until you've sold all your previous, which means you're probably selling at a loss and buying it at a higher price than when your mind actually changed, especially if the reason your mind changed is because some news went public, which affects EVERYONE'S predictions.

Arbitrage does exist on the site, though.  Romney announced almost a week ago that he isn't running, but NO was still for sale at 93 cents.  It isn't A LOT of arbitrage, but with a lot of those situations, you could probably get some easy, albeit small, profit.

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