Creditworthiness dynamics and Hidden Markov Models

A dynamic monitoring of credit risky portfolios is described. In the first section, it is shown how a Markov dependence can be used in modelling the borrower's behaviour: a chain of transition probabilities matrices is built in which the states of the dynamic stochastic system are the number of instalments in arrears. In the second part, such a model is generalized in the framework of the Hidden Markov Models to explain how the credit market conditions could affect the borrower's payment process. Numerical examples complete the note.