Models.Behaving.Badly. Cover


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


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.

Praise For Models.Behaving.Badly.

“A readable, even eloquent combination of personal history, philosophical musing and honest confession concerning the dangers of relying on numerical models not only on Wall Street but also in is undeniable that Models.Behaving.Badly. itself performs splendidly.” —Burton Malkiel, Wall Street Journal

"An erudite yet pleasantly readable exploration of why financial models failed during the U.S. mortgage meltdown and why modelers must learn to use them more wisely. Derman has distilled a lifetime of reading, research and thinking into these pages, and I read the book twice to see how he pulled the threads together without losing the reader." Bloomberg News

"Ranging wittily across philosophy, literature, and the arcane world of high finance, Derman's argument is a heady mix of physics, economics, and memoir." Nature

“A fascinating cross-disciplinary exploration of how and why financial and scientific models fail…A unique examination of the limits of models and theories in understanding and predicting human behavior, and a nice rejoinder to the equations-can-solve-or-explain-everything crowd.” Kirkus Reviews

Emanuel Derman has written my kind of a book, an elegant combination of memoir, confession, and essay on ethics, philosophy of science and professional practice. He convincingly establishes the difference between model and theory and shows why attempts to model financial markets can never be genuinely scientific. It vindicates those of us who hold that financial modeling is neither practical nor scientific. Exceedingly readable.” —Nassim N. Taleb, author of The Black Swan

"This is a compelling, accessible and provocative piece of work, that forces us to question many of the assumptions that we work with. As Derman explains so clearly, models are not "bad" in themselves; on the contrary, they are crucial for modern society. However, they have been used in a dangerously sloppy and careless way, with sometimes terrible results. Derman explains this clearly, and draws heavily onhis own lifetime experiences - ranging from growing up in appartheid south africa, working in the scientific field and then as a financial engineer on wall street - to provide a moving and fascinating set of illustrations of these principles. The conclusion is unexpectedly otpimistic - if people choose to listen." —Gillian Tett, author of Fool's Gold

"Models. Behaving. Badly. is an engaging and personal meditation on the limitations of our ability to predict the future, especially—but not only—in the context of financial markets. He is not interested in blame or politics, but in the deeper lessons to be drawn from the financial crisis. As a physicist who was also highly placed in the financial world, he explains clearly the difference between prediction and advice, theory and model and knowledge and wisdom." —Lee Smolin, Senior Researcher at Perimeter Institute for Theoretical Physics, author of The Trouble with Physics; Life of the Cosmos, and Three Roads to Quantum Gravity

"If you don't want your models to behave badly, you should study carefully these words of wisdom on the philosophy of quantitative modeling. Emanuel Derman has always been one of the most respected quants on Wall Street.  Now he has proven that he is also one of the most thoughtful. Though, in the sequel he should tell us what happened to the large man over the Sudan!"
—Clifford S. Asness, Ph.D., Managing & Founding Principal AQR Capital Management

“I found this book fascinating. Derman has a skill of mixing the personal with the abstract. You will not find another that takes you from the vagaries of the human eye to the vagaries of the stock market with stops at quantum electrodynmics. It is quite a ride.” —Jeremy Bernstein, author of Quantum Leaps, and Plutonium

"This is a thoughtful book for anyone interested in the overlap between the hard sciences and the soft sciences, from physicists to bankers. But finance academics beware, Professor Derman, with an iron fist in a velvet glove, gives them a good slapping." —Paul Wilmott, co-author "Financial Modelers' Manifesto"

Praise for Emanuel Derman’s My Life as a Quant:

"There are few "gentlemen bankers" left these days. That is why Emanuel Derman's memoirs are so compelling…Derman's wry humour and sense of irony are apparent throughout the book." Financial Times

"That sense of being an intruder in outlaw territory lends an intriguing mood to Derman's My Life as a Quant, a literate and entertaining memoir." BusinessWeek

“Reads like a novel, but tells a lot about brains applied to making money grow.” —Paul A. Samuelson, MIT, Nobel Laureate in Economic Sciences