Rajiv Sethi looks at an apparent attempt to manipulate prediction markets on election day:
Prediction Market Manipulation: A Case Study: ...beliefs that one's candidate of choice has lost can affect turnout. It has been argued, for instance, that early projections of victory for Reagan in 1980 depressed Democratic turnout in California, and that Republican turnout in Florida was similarly affected in 2000 when the state was called for Gore while voting in the panhandle was still underway. For this reason, early exit poll data is kept tightly under wraps these days, and states are called for one candidate or another only after polls have closed.
This effect of beliefs on behavior implies that a candidate facing long odds of victory has an incentive to inflate these odds and project confidence in public statements, lest the demoralizing effects of pessimism cause the likelihood of victory to decline even further. Traditionally this would be done by partisans on television sketching out implausible scenarios and interpretations of the incoming data to boost their supporters. But with the increasing visibility of prediction markets, this strategy is much less effective. If a collapse in the price of a contract on Intrade reveals that a candidate is doing much worse than expected, no amount of cheap talk on television can do much to change the narrative. ...
Let me break in here and note this was the point of Mittmentum, to make momentum in the campaign a self-fulfilling prophecy -- create the appearance of a bandwagon even though it doesn't actually exist, and wait for people to jump on and make the bandwagon a reality. Unfortunately for them, evidence got in the way (this is where the Moneyball analogy breaks down -- baseball scouts do not have the ability to create a reality with their tales and intuition, political pundits do, or I guess I should say did after yesterday's triumph of data over punditry). Anyway:
Given this, the incentives to interfere with what the markets are saying becomes quite powerful. Even though trading volume has risen dramatically in prediction markets over recent years, the amount of money required to have a sustained price impact for a few hours remains quite small, especially in comparison with the vast sums now spent on advertising.
In general, I believe that observers are too quick to allege manipulation when they see unusual price movements in such markets. As I noted in an earlier post, a spike in the price of the Romney contract a few days ago was probably driven by naive traders over-reacting to rumors of a game-changing announcement by Donald Trump... If one really wants to manipulate a market, it has to be done by placing large orders that serve as price ceilings and floors, and to do this across complementary contracts in a consistent way.
As it happens, this is exactly what someone tried to do yesterday. ... [presents evidence] ...
Since the exchange requires traders to post 100% margin (to cover their worst case loss and eliminate counterparty risk), the funds required to place these orders was about $240,000 in total. A non-trivial amount, but probably less than the cost of a thirty-second commercial during primetime.
Could this not have been just a big bet, placed by someone optimistic about Romney's chances? I don't think so, for two reasons. First, if one wanted to bet on Romney rather than Obama, much better odds were available elsewhere... More importantly, one would not want to leave such large orders standing at a time when new information was emerging rapidly; the risk of having the orders met by someone with superior information would be too great. Yet these orders stood for hours, and effectively placed a floor on the Romney price and a ceiling on the price for Obama....
Should one be concerned about such attempts at manipulation? I don't think so. They muddy the waters a bit but are transparent enough to be spotted quickly and reacted to. ... Attempts at manipulating beliefs are nothing new in presidential politics, it's just the methods that have changed. And as long as one is aware of the possibility of such manipulation, it is relatively easy to spot and counter. The same social media that transmits misinformation also allows for the broadcast of countervailing narratives. In the end the fog clears and reality asserts itself. Or so one hopes.