问一下reduce form 的缺点

Marlin asks Betta if reduced form models of corporate credit risk provide advantages over structural models. Betta responds that reduced form models have less restrictive assumptions than structural models because of the one critical assumption that cannot be relaxed. He notes two weaknesses with regard to reduced form models: (1) The use of past observations to predict the future requires that it be formulated and back tested properly, and (2) credit risk measures are biased by implicit estimation procedures.

Finally, Betta would like to examine the term structure of credit spreads for Bay Corp. The company has a number of coupon bonds outstanding across the maturity spectrum that should facilitate his analysis. He notices the market prices of the bonds are lower than would be implied by results of either a structural or reduced form model. Betta is confident he has correctly estimated the price of the zero-coupon bonds implied by the coupon bond prices, which in this case rank equally in the capital structure.