Unfortunately, no precise mathematical model can determine correlation across securities, which is always an educated guess based mostly (sometimes entirely) on past behavior. Thus, the explosion of CDOs in the United States during the housing boom was predicated upon the shaky assumption that house prices never fall nationwide.
遗憾的是，不存在哪种精确的数学模型可以确定不同证券的关联性，过往表现一直是确定证券关联性最可靠（有时甚至是唯一）的依据。 因此，美国房地产市场繁荣阶段债务抵押债券的迅猛发展是以“房地产价格不会在全国范围内出现下降”这一靠不住的假设为前提。