Credit Ratings in Structured Finance and the Role of Systemic Risk
Bank of Italy
September 15, 2010
Bank of Italy Temi di Discussione (Working Paper) No. 774
This paper explores the implications of systemic risk in Credit Structured Finance (CSF). Risk measurement issues loomed large during the 2007-08 financial crisis, as the massive, unprecedented number of downgrades of AAA senior bond tranches inflicted severe losses on banks, calling into question the credibility of Rating Agencies. I discuss the limits of the standard risk frameworks in CSF (Gaussian, Single Risk Factor Model; GSRFM), popular among market participants. If implemented in a ‘static’ fashion, GSRFM can substantially underprice risk at times of stress. I introduce a simple ‘dynamic’ version of GSRFM that captures the impact of large systemic shocks (e.g. financial meltdown) for the value of CSF bonds (ABS, CDO, CLO, etc.). I argue that a proper 'dynamic' modeling of systemic risk is crucial for gauging the exposure to default contagion (‘correlation risk’). Two policy implications are drawn from a 'dynamic' GSRFM: (i) when rating CSF deals, Agencies should disclose additional risk information (e.g. the expected losses under stressed scenarios; asset correlation estimates); and (ii) a ‘point-in-time’ approach to rating CSF bonds is more appropriate than a ‘through-the-cycle’ approach.
Number of Pages in PDF File: 66
Keywords: structured finance, systemic risk, credit risk measures, bond pricing
JEL Classification: E44, E65, G01, G12, G13, G14, G18, G21, G24, G28, G34working papers series
Date posted: March 24, 2011
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