The situation of a limited availability of historical data is frequently encountered in portfolio risk estimation, especially in credit risk estimation. This makes it, for example, difficult to find temporal structures with statistical significance in the data on the single asset level. By contrast, there is often a broader availability of cross-sectional data, i.e., a large number of assets in the portfolio. This paper proposes a stochastic dynamic model which takes this situation into account. The modelling framework is based on multivariate elliptical processes which model portfolio risk via sub-portfolio specific volatility indices called portfolio risk drivers. The dynamics of the risk drivers are modelled by multiplicative error models (MEM) -as introduced by Engle (2002) -or by traditional ARMA models. The model is calibrated to Moody's KMV Credit Monitor asset returns (also known as firm-value returns) given on a monthly basis for 756 listed European companies at 115 time points from 1996 to 2005. This database is used by financial institutions to assess the credit quality of firms. The proposed risk drivers capture the volatility structure of asset returns in different industry sectors. A characteristic temporal structure of the risk drivers, cyclical as well as a seasonal, is found across all industry sectors. In addition, each risk driver exhibits idiosyncratic developments. We also identify correlations between the risk drivers and selected macroeconomic variables. These findings may improve the estimation of risk measures such as the (portfolio) Value at Risk. The proposed methods are general and can be applied to any series of multivariate asset or equity returns in finance and insurance.Key words: Portfolio risk modelling, Elliptical processes, Credit risk, multiplicative error model, volatility clustering, Moody's KMV Credit Monitor database.
JEL classification: C51, C16, C13
Non-technical summaryOver the past years, the availability of data for financial analysis in general and portfolio risk analysis in particular has substantially improved. This situation enables the use of more sophisticated methods for portfolio management and risk analysis and has attracted many scholars from the industry, academia, and banking supervision.The present research project proposes a multidimensional stochastic dynamic model that identifies portfolio risk drivers via volatilities in two dimensions, over time and across industry sectors. The identification and the need of modelling volatility dynamics in financial data goes (at least) back to the research by the Nobel laureate Robert Engle and has gained importance during the last two decades. The volatility is often referred to as the key driver of risk in a financial portfolio, and many performance measures or risk measures express the amount of risk via the volatility.The model is applied to market-based credit risk data (monthly asset returns also known as firm-value returns) covering a limited period of time but comprising a large number of assets. T...