Credit Ratings in Structured Finance and the Role of Systemic Risk

Abstract:     
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, G34

working papers series