Brad Plumer at the Wonkblog discusses a recent attempt to manipulate Intrade.

On Monday night, after the debate, Barack Obama was leading Romney on Intrade by around 60 percent to 40 percent. But at around 10:00 a.m. on Tuesday morning, Romney surged to 48 percent. Was this evidence that the conventional wisdom was wrong? Had Romney actually won the debate handily? Or, alternatively, was the nosedive in the stock markets putting a dent in Obama’s re-election chances?

Neither. As economist Justin Wolfers pointed out on Twitter, the huge swing toward Romney appears to have been driven by a single trader who spent about $17,800 buying up Romney shares and pushing the Republican candidate’s chances on Intrade up to 48 percent. But the surge only lasted a few minutes before other traders whittled the price back down to what they saw as a more accurate valuation. Romney’s odds of winning are currently back at around 41 percent.