Skip navigation


Giacomo John Roma pointed me to an interesting article by Taleb & Spitznagel as part of the LinkedIn discussion and here are my thoughts on this and the related discussion.

I infer that Taleb’s primary concern is leverage. Debt provides leverage, and unconstrained debt provides unconstrained leverage. That is the lesson of 2008. Taleb wants us to reduce the extent of the leverage in our economy, because debt has a property that affects our perception of risk, i.e. debt hides volatility.

Regarding VaR:

(1) If you examine the historical data, outside of social sciences and quality control, there are very few thing that are Normally distributed. Taleb’s point here is that much of the mathematics that is used in finance and economics is based strongly on the assumptions of normality, and therefore, are not good forecasters of their metrics. They only appear to work when the law of large numbers can be applied. Therefore Taleb is recommending that a lot of these mathematics and their resulting analytical tools are erroneous in the long run.

(2) There are serious problems with VaR even without the normality assumption. In my experiece (I never assume normality) with years of building econometric CMBS loss and default models I found that VaR would consistently underestimate losses in the first 3 to 5 years of the loan.

Black Swans are a real problem in mortgages. The historical data shows that they are real. Just look at 2008. My own estimates are that Black Swans in CMBS bonds are on the order of 20% to 80%.

I also found that the only realistic way to handle undisciplined leverage was to implement non-linear economic or risk capital controls. This comes back to Taleb’s point on non-linearity.

Non-linearity is not new. Credit card companies use non-linearity a lot. They impose 2x and even 3x or 30% rates on delinquent card holders. Try imposing that on institutions, and all hell breaks loose. This is the power of buyers and sellers at play, not mathematics and not finance.

___________________________________________________________________
Disclosure: I’m a capitalist too, and my musings & opinions on this blog are for informational/educational purposes and part of my efforts to learn from the mistakes of other people. Hope you do, too. These musings are not to be taken as financial advise, and are based on data that is assumed to be correct. Therefore, my opinions are subject to change without notice. This blog is not intended to either negate or advocate any persons, entity, product, services or political position.
___________________________________________________________________

Advertisements

One Comment

  1. Through the magic of wordpress’ KNN thingee, it informed me that I was also in that linkedin discussion:

    http://scottlocklin.wordpress.com/2009/07/17/nassim-taleb-clown-of-quantitative-finance/


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

%d bloggers like this: