Amplified mortgage portfolio super seniors: a really bad idea

The UBS shareholder report on the firm's subprime losses makes fascinating reading and I will try to return to it later in the week. Meanwhile however it is worth noting that a major cause of the UBS losses were AMPs. Let the report take up the story:

[AMPs] were Super Senior positions where the risk of loss was initially hedged through the purchase of protection on a proportion of the nominal position (typically between 2% and 4% though sometimes more). This level of hedging was based on statistical analyses of historical price movements that indicated that such protection was sufficient to protect UBS from any losses on the position.

Let's try and tease this apart. The bank is long the supersenior tranche in a CMO. They 'hedged' this position by buying credit protection on the underlying mortgage portfolio in an amount calculated to minimise short term P/L volatility. I think.

Isn't this pure gaming of the VAR model? This 'hedge' dramatically reduce the VAR. But losses build up in the junior and rise through the mezz, the bank will need to short a larger and larger percentage of the underlying mortgages to remain hedged. In other words this position is massively short credit convexity even if it is credit delta neutral. And even that is assuming that you can short more of the underlying pool into a falling market, an assumption that is highly questionable.

Anyway, even if the AMPs position was not designed to game the VAR model, it certainly achieved that effect:

Once hedged, either through NegBasis or AMPS trades, the Super Senior positions were VaR and Stress Testing neutral (i.e., because they were treated as fully hedged, the Super Senior positions were netted to zero and therefore did not utilize VaR and Stress limits). The CDO desk considered a Super Senior hedged with 2% or more of AMPS protection to be fully hedged. In several MRC reports, the long and short positions were netted, and the inventory of Super Seniors was not shown, or was unclear.

(See here for a discussion of negative basis trading.) For something like this there is real danger that the system's view is seen as the only reality. If the VAR model says there is no risk, the firm might actually think that's true.

Next we come to model risk:

The AMPS model was certified by IB [UBS investment bank] Quantitative Risk Control...but with the benefit of hindsight appears not to have been subject to sufficiently robust stress testing. [...] The cost of hedging through a Negative Basis trade was approximately 11 bp, whereas the cost of hedging through an AMPS trade was approximately 5 – 6 bp.

So, a positive carry asset hedged very cheaply but leaving a large short gamma position which was not captured by the firm's risk model. They really were asking to be creamed by a big market move. And then one came along.