Monday, 20 July 2009

A small town in Switzerland, part 3

Glorious, glorious, glorious is the day: yet more Basel. Here's a key passage from BCBS158:
Factors that are deemed relevant for pricing should be included as risk factors in the value-at-risk model.
If you took the committee at its word, here, no one would have a VAR model. Just consider an equity derivatives book on underlyings in the Eurostoxx. There are 50 underlyings, 50 dividend yields (more if you consider the term structure of dividend yields), at least 20 interest rates in Euros, and as many implied volatilities as you have (strike, maturity) pairs for your options. A decent sized book will have many hundreds, perhaps many thousands, of risk factors. No one has a VAR model with all of those factors in it. So, what is a bank to do? Let's turn back to the committee:
Where a risk factor is incorporated in a pricing model but not in the value-at-risk model, the bank must justify this omission to the satisfaction of its supervisor.
Ah lovely. So if you have a tolerant supervisor, perhaps because you are in a small country, or because you are a national champion bank, all is well. If not, you will have some hoops to jump. This provision in short is a charter for regulatory arbitrage. The next part is even worse:
In addition, the value-at-risk model must capture nonlinearities for options and other relevant products (e.g. mortgage-backed securities, tranched exposures or n-th-to-default credit derivatives), as well as correlation risk and basis risk (e.g. between credit default swaps and bonds). Moreover, the supervisor has to be satisfied that proxies are used which show a good track record for the actual position held (i.e. an equity index for a position in an individual stock).
If this doesn't make players with big trading books redomicile to somewhere small, low tax and friendly, I don't know what will.

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