Regulatory capital for trading book positions includes two components that cover different
risks but apply to the same portfolio, one for market risk and one for credit risk. Similar
approaches are common in banks’ internal models for economic capital. Although it is known
that joint market and credit risk of certain investments can be larger than the sum of risks,
the problematic cases identified so far have been relatively exotic. I show that very common
investments – corporate bond holdings or CDS portfolios – are also affected. There are
realistic conditions under which credit risk (represented by ratings and default) and spread
risk (represented by rating specific spread indices) combine to a total value-at-risk (VaR)
50 percent larger than the sum of spread and credit VaR; this effect is even stronger for
the expected shortfall. If migration risk is segregated from default risk and incorporated
into spread risk, as recently put forward by the Basel Committee, total risk is no longer
underestimated. Furthermore, I improve a theoretic result of Breuer et al. (2010) that
defines a sufficient condition under which risk separation is harmless.
Steht auch als Elektronisches Dokument zur Verfügung (ISBN 978-3-95729-164-6)
Peter Raupach
Eigenkapitalregulierung Handelsbuch Risikomessung