Barron's [subscription required] revealed some scary statistics about this week's carnage. The smartest of the smart are finding that their computer models are telling them to do the wrong things at the moment of maximum peril. As a result, The Goldman Sachs Group's (NYSE: GS) $8 billion Global Alpha hedge fund is down 26% so far this year and the $26 billion Renaissance Institutional Equities Fund -- run by the $1.7 billion (2006 compensation) man, James Simons -- has fallen 8.7% so far this month.

What is going on? The computer models that run these funds don't model what is happening now -- a simultaneous dash to liquidate by all their peers. Statistical factor-based quantitative models -- which weight dozens of valuation, growth, and momentum variables to create long/short portfolios -- have attracted many competitors.

Their models broke in recent weeks as volatility surged, leverage was cut back, heavily shorted stocks went up and statistically cheaper shares cracked. One anonymous manager said "There is this unknown risk, when there are enough people doing what you do, that when some of them have to unwind and they start unwinding -- you are just going to get crushed. And that's not in the model anywhere."