Sovereign Bond-Backed Securities : A VAR-for-VaR and Marginal Expected Shortfall Assessment

The risk reducing benefits of the sovereign bond-backed security (SBBS) proposal of Brunnermeier et al. (2016) have been assessed in terms of the likely losses that different kinds of holders would suffer under simulated default scenarios. However, the effects of mark-to-market losses that may occur when there is rising uncertainty about defaults, or when self-fulfilling destablising dynamics are prevalent, have not yet been examined. We apply the “VAR-for-VaR” method of Manganelli et al. (2015) and the Marginal Expected Shortfall (MES) approach of Brownlees and Engle (2012, 2017) to estimated yields of SBBS to assess how ex ante exposures and marginal contributions to systemic risk are likely to play-out for different SBBS tranches under various securitisation structures. We compare these with exposures/MES of single sovereigns and a diversified portfolio of sovereigns. We find that the senior SBBS has extremely low ex ante tail risk and that, like the low-risk sovereigns, it acts as a hedge against extreme market-wide yield movements. The mezzanine SBBS has tail risk exposure similar to that of Italian and Spanish bonds. Yields on SBBS appear to be adequate compensation for their risks when compared with single sovereigns or a diversified portfolio