Structural Model of Credit Risk - Distance-to-Default

To talk about the Distance-to-Default, we would like to discuss approaches about the credit risk analytics in econometrics. In econometrics, there are two common approaches to construct a model. One is the structural model, the other is reduced model. The main difference is the structural model is estimated in their theoretically given form, however, as for reduced form model is estimated by the exogenous variables.To talk about the Distance-to-Default, we would