"Housing prices had never before fallen as far and as fast as they did beginning in 2007. But that's what happened. Former Federal Reserve chairman Alan Greenspan explained to a congressional committee after the fact, "The whole intellectual edifice, however, collapsed in the summer of [2007] because the data input into the risk management models generally covered only the past two decades, a period of euphoria. Had instead the models been fitted more appropriately to historic periods of stress, capital requirements would have been much higher and the financial world would be in far better shape, in my judgment."3"