Another day of market volatility

The Dow finished the day up 69 points, which is a big turnaround from earlier in the day, when the index was down more than 100 points. Market watchers are running out of explanations on why stocks are so volatile. From the NYT:

Some economists say they fear the volatility may feed upon itself. The violent ups and downs, said Robert Shiller, an economics professor at Yale, may in turn undermine confidence in the economy, and the weakness in the economy can lead to more strident politics -- all of which feeds the volatility loop. "It is not well understood why we have these bursts of volatility," Mr. Shiller said. "It seems that in these rare periods of bad economic performance and anxiety about the economy, we have volatility in the markets and high volatility in the political arena. Bad things can happen. This worries me."