They define four credit risk categories and they define a formula involving the amount of assets in each of the categories.

他们定义了四个风险等级,然后根据每个风险等级下的资产额,定义了一个资产总额的计算公式

耶鲁公开课 - 金融市场课程节选

When you do these calculations, which I just did for insurance-- I was talking about insurance companies-- assuming that risks are independent, everything's independent and we've got it all figured out.

当你试图去,做保险相关计算时,我指的是保险公司...,假定风险是独立的,事件都是独立的,可以算出一个结果

耶鲁公开课 - 金融市场课程节选