Ebnöther, Silvan, Paolo Vanini, "Credit Portfolios: What defines risk horizons and risk measurement?", Journal of Banking & Finance, Vol. 31, No. 12, (December 2007), pp. 3663-3679.
Abstract: The strong autocorrelation between economic cycles demands that we analyze credit portfolio risk in a multiperiod setup. We embed a standard one-factor model in such a setup. We discuss the calibration of the model to Standard & Poor's ratings data in detail. But because single-period risk measures cannot capture the cumulative effects of systematic shocks over several periods, we define an alternative risk measure, which we call the time-conditional expected shortfall (TES), to quantify credit portfolio risk over a multiperiod horizon.
Keywords: Credit-risk management, Portfolio management, Risk measurement, Coherence, VaR, Expected shortfall, Factor model.