This is a sequel of sorts to the author's 1992 "Capital Ideas," but it also functions nicely as a sequel to the Fischer Black biography I just finished. Both earlier books trace the rise of financial theory from Harry Markowitz's 1952 article showing how diversification maximizes returns while reducing risks, through to the Black-Scholes model for pricing stock options. The loci of all these ideas were the Capital Asset Pricing Model (CAPM) and the efficient market hypothesis, both of which seemed to claim that no one could consistently beat the market. The irony of this book is it explains how these ideas about efficient markets spawned an entire world of traders and dealers who used those models to find out exactly how they could beat the market.
At the Yale Endowment Fund David Swenson realized alternative assets like venture capital and hedge funds were often excluded from definitions of "the market," so investors could benefit from over-weighting these. Martin Leibowitz, the absurdly prolific writer and trader at Salomon Brothers and TIAA-CREF, found out that almost all variability in a portfolio came from equities and other assets that varied in their returns along with equities, and thus moving funds to assets like Real Estate Investment Trusts could provide a return that didn't tend to co-vary with stocks. By diversifying in this way he could both lower risks and increase total returns. Even Harry Markowitz himself moved to Wall Street and found that market distortions like the Federal Reserve's Regulation T, which limits short selling, offered inefficient opportunities to exploit.
Here, all the revolutionaries who came to bury Wall Street's work as mere "interior decoration," as James Tobin called it, ended up instead creating a new one. While once they thought dealers only feasted parasitically on an efficient market, now they joined the feast. Their insights that the real value of stocks or bonds is not due to their individual value but how much or how little they "co-varied" with the whole market, often called the asset's "beta," seemed to offer an exciting cornucopia of new investment possibilities. Finding the market's inefficiencies with regard to particular asset's value also allowed them to find more returns than the market would seem to warrant, often called a stock's "alpha." If one wonders how "searching for alpha" became the cynosure of modern stock traders, this book explains it. The other irony of this book though is that by finding all these inefficiencies (such as the under-appreciation of alternative assets), these traders and academics gradually eliminated them, and thus made the market further approach the original theory they all started with.
Of course hanging over this entire book, published in 2007, is the specter of the financial crisis. How efficient were all these financial engineers in the end one has to ask, however important their ideas were? Far too much of this book is also taken up with Bernstein's interviews with these men, and many of these only repeat the same points. The book constantly references back to "Capital Ideas" and is thus something of more an addendum to that book than a true sequel. Yet once again, the ideas here are shown to have both surprising corollaries and relevance, and to have shaped our world more than we would think.