went into the most detail was, unfortunately, also hard to follow. Your article spreads a little more light on it. Seems JP Morgan pushed for a change in pricing in 2004, but their new model model didn't figure in compound blow-ups in corporate credit. Most of the hedge funds out there made adjustments for this while the big banks proprietary desks didn't. So most of this panic is taking place on the bankers' desks. Least that's what I get out of it. Something happened that made them (banks) see the error in their model. I've got a feeling that maybe the Dura CDS settlement somehow shed light and opened some eyes - investors are not being compensated for their risks. Here's a couple of the articles from yesterday. The first one is on Dura, seems like it's a test run of some sort. The second is that long, detailed article.
http://today.reuters.com/news/articleinvesting.aspx?view=CN&storyID=2006-11-06T154606Z_01_L06398127_RTRIDST_0_MARKETS-DERIVATIVES-DURA.XML&rpc=66&type=qcnahttp://www.risk.net/public/showPage.html?page=351397snip>
"We worry about how much the apparent liquidity in the credit derivatives market is being driven by structured trades," says a New York-based senior risk manager at a US securities dealer. "Our sense is the active trading of structured credit is actually confined to a fairly small number of market participants. There are not hundreds and hundreds of people trading tranches. Quite a lot of that trading actually happens on banks' proprietary desks as far as we can see, and that's a little weird."
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Market replication
Bespoke CDO tranches first emerged in the early part of this decade, giving investors the ability to choose the credits in the collateral, the trade maturity, the attachment points (the amount of subordination below the tranche), the tranche width, the rating, the rating agency and the format (funded or unfunded). And the emergence of a liquid, two-way index tranche market in 2003 gave the prospect of efficient price discovery for tranches, enabling participants to infer implied correlation from market prices to determine relative value.
Dealers typically use base correlation for pricing CDO tranches. This approach emerged in 2004, championed by JP Morgan, and was widely seen as responding to shortcomings of compound correlation. Under the compound correlation approach, a model (usually a Gaussian copula) takes all single-name spreads and a single-asset correlation as inputs and produces a tranche spread. As in the options market, where implied volatility is calculated by backing market prices through the Black-Scholes model, an implied correlation can be calculated from traded spreads, using the Gaussian copula model. In essence, compound correlation can be defined as the single correlation that matches the value of a tranche to a market spread.
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Unlike compound correlation, base correlation only has one solution for a particular spread level. That's because each tranche is effectively a first loss that combines all the tranches up to the detachment point, and the equity tranche spread is a monotonic function of correlation - the spread on the equity tranche falls as correlation rises. Base correlation also exhibits a well-defined skew - where implied correlations differ according to tranche. One of the benefits of this approach over compound correlation is that it is easy to interpolate the base correlation curve to value non-standard tranches.
These base correlations are used in the valuations of bespoke tranches. In simple terms, the dealer typically attempts to find an equivalent index tranche and uses that base correlation in the pricing of the bespoke CDO tranche.
Top academics and quants, however, are far from happy with the results of the base correlation approach. For a start, the large pool model uses a number of simplified assumptions for calculating base correlation - for instance, the model assumes an equally weighted portfolio of credits with the same default probability and a constant recovery rate, normally 40%. The model does not consider individual spreads for all the credits in the portfolio, and so does not properly account for blow-ups in a few names - something that occurred last May with the downgrade of Ford and General Motors. Bespoke portfolios are also likely to contain different credits from the indexes on which the base correlation measure is based - for instance, bespoke portfolios could include a mix of European and US names - which could create imprecisions in valuations.
In addition, because the base correlation is calculated as the implied correlation of an equity tranche that includes all tranches up to the detachment point, it's difficult to extract relative-value information among individual tranches. It can also sometimes cause the base correlation curve to move in counter-intuitive ways as spreads of individual tranches fluctuate.