Why Confusing Illusion with Reality Can Lead to Disaster, on Wall Street and in Life

By Emanuel Derman
(Free Press, Hardcover, 9781439164983, 240pp.)

Publication Date: October 25, 2011

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Emanuel Derman was a quantitative analyst (Quant) at Goldman Sachs, one of the financial engineers whose mathematical models usurped traders' intuition on Wall Street. The reliance traders put on such quantitative analysis was catastrophic for the economy, setting off the series of financial crises that began to erupt in 2007 with the mortgage crisis and from which we're still recovering. Here Derman looks at why people--bankers in particular--still put so much faith in these models, and why it's a terrible mistake to do so.

Though financial models imitate the style of physics by using the language of mathematics, ultimately they deal with human beings. Their similarity confuses the fundamental difference between the aims and possible achievements of the phsyics world and that of the financial world. When we make a model involving human beings, we are trying to force the ugly stepsister's foot into Cinderella's pretty glass slipper.  It doesn't fit without cutting off some of the essential parts. Physicists and economists have been too enthusiastic to recognize the limits of their equations in the sphere of human behavior--which of course is what economics is all about. 

Models.Behaving.Badly includes a personal account Derman's childhood encounter with failed models--the utopia of the kibbutz, his experience as a physicist on Wall Street, and a look at the models quants generated: the benefits they brought and the problems they caused. Derman takes a close look at what a model is, and then he highlights the differences between the success of modeling in physics and its relative failure in economics.  Describing the collapse of the subprime mortgage CDO market in 2007, Derman urges us to stop relying on these models where possible, and offers suggestions for mending these models where they might still do some good.  This is a fascinating, lyrical, and very human look behind the curtain at the intersection between mathematics and human nature.

About the Author
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.
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