Mutualising sovereign bonds is equivalent to forming a linear combination of the underlying bonds, i.e. a portfolio of them. Hence the risk associated to the portfolio is a function of the risks of the constituents and their correlations.
- In tranquil periods these risks have a linear nature,
- In periods of turmoil non-linearities appear, namely due to extreme events, that induce non-linear -or tail- risks.
Figure 1 shows the quarterly cross-sectional average correlations (from 2005Q1 to 2012Q2) for the Sovereign bond yields of all the Eurozone countries (solid blue), the core countries (dotted red), the peripheral countries (doted and dashed green), and the peripheral countries but Greece (dashed purple).
Prior to the crisis correlations were very close to unity, reflecting the almost perfect co-movements among the yields. Since the beginning of the crisis the correlations have sharply decreased for all countries and groups of countries. From a risk perspective, the creation of the Eurobonds may be seen as appropriate since the benefits (creditworthiness, resilience, stability, and liquidity) offset the slight increase of risk associated to the small correlations.