There’s Enough Math in Finance Already. What’s Missing is Imagination.
EMANUEL DERMAN is Head of Risk at Prisma Capital Partners and a professor at Columbia University, where he directs their program in financial engineering. He is the author of My Life As A Quant, one of Business Week's top ten books of the year, in which he introduced the quant world to a wide audience.
He was born in South Africa but has lived most of his professional life in Manhattan in New York City, where he has made contributions to several fields. He started out as a theoretical physicist, doing research on unified theories of elementary particle interactions. At AT&T Bell Laboratories in the 1980s he developed programming languages for business modeling. From 1985 to 2002 he worked on Wall Street, running quantitative strategies research groups in fixed income, equities and risk management, and was appointed a managing director at Goldman Sachs & Co. in 1997. The financial models he developed there, the Black-Derman-Toy interest rate model and the Derman-Kani local volatility model, have become widely used industry standards.
In his 1996 article Model Risk Derman pointed out the dangers that inevitably accompany the use of models, a theme he developed in My Life as a Quant. Among his many awards and honors, he was named the SunGard/IAFE Financial Engineer of the Year in 2000. He has a PhD in theoretical physics from Columbia University and is the author of numerous articles in elementary particle physics, computer science, and finance.
And so for example, if you’re building an option model, you’re saying, what will volatility be in the future? And given my estimate of volatility in the future, I can value an option today. If you’re looking at CDO’s, which sort of came in a cropper in the big financial crisis, essentially human beings are saying, what will housing prices do in the future? What will defaults on loans be and defaults on mortgages be? And given my imagined scenario for the future, what should
I pay for something today that’s sensitive to that future behavior?
The big failures, I think, are failures of imagination, not of mathematics. The big mistakes are when you don’t’ think of something that does come to fruition eventually.
When I was in graduate school, I went to see a movie the night before my qualifying exams called, “Bedazzled” with Peter Cook and Dudley Moore. It’s about 40 years old, but I think it was remade a few years ago. Dudley Moore - I think they’re both dead now, Dudley Moore and Peter Cook - he was a short-order cook at a Wimpy’s in London and he’s in love with the waitress that serves him. Peter Cook plays the devil and offers him seven chances to seduce the waitress in exchange for his soul. And so he agrees. And then he tries to specify the circumstances under which he will be with the waitress. And so the first time, he says something like, he’d like to be in a fancy castle in Oxfordshire and with her and both of them in love with each other and both of them wealthy. And the devil snaps his fingers, and there they are in this castle and they’re around the billiard table and they’re in love with each other, but she’s married to the owner of the castle and he’s just a guest. And she has scruples, so she’s not willing to get involved with him.
And in every scenario he tries of these seven scenarios he gets it wrong. In the last one he asks if they can both just be somewhere quiet with nobody to interfere with them and nobody talking, and they make them both nuns in a sort of Trappist monastery.
And so his imagination can never specify precisely enough the future that he’d like to have. And I think that’s sort of what goes wrong with a lot of financial models. You can’t really write down one short description of all the things that markets may do in the future.
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