Monday, October 14, 2013

Fama, Hansen, and Shiller Nobel

Gene Fama, Lars Hansen and Bob Shiller win the Nobel Prize. Congratulations! (Minor complaint: Nobel committee, haven't you heard of Google? There are lots of nice Gene Fama photographs lying around. What's with the bad cartoon?)

I'll write more about each in the coming days. I've spent most of my professional life following in their footsteps, so at least I think I understand what they did more than for the typical prize.

As a start, here is an an introduction I wrote for  Gene Fama’s Talk, “The History of the Theory and Evidence on the Efficient Markets Hypothesis” given for the AFA history project. There is a link to this document on my webpage here. The video version is here at IGM.

Introduction for Gene Fama

On behalf of the American Finance Association and the University of Chicago Graduate School of Business, it is an honor and a pleasure to introduce Gene Fama. This talk is being videotaped for the AFA history project, so we speak for the ages.

Gene will tell us how the efficient-markets hypothesis developed. I’d like to say a few words about why it’s so important. This may not be obvious to young people in the audience, and Gene will be too modest to say much about it.

“Market efficiency” means that asset prices incorporate available information about values. It does not mean that orders are “efficiently” processed, that prices “efficiently” allocate resources, or any of the other nice meanings of “efficiency.” Why should prices reflect information? Because of competition and free entry. If we could easily predict that stock prices will rise tomorrow, we would all try to buy today. Prices would rise today until they reflect our information.

This seems like a pretty simple “theory,” hardly worth all the fuss. Perhaps you expect general relativity, lots of impenetrable equations. Gene is more like Darwin, and the efficient markets hypothesis is more like evolution. Both evolution and efficient markets are elegant, simple, and powerful ideas that organized and energized vast empirical projects, and that’s the true measure of any theory. Without evolution, natural history would just be a collection of curious facts about plants and animals. Without the efficient markets hypothesis, empirical finance would just be a collection of Wall-Street anecdotes, how-I-got-rich stories, and technical-trading newssheets.

Efficient-market theory and empirical work are also a much deeper intellectual achievement than my little story suggests. There are plenty of hard equations. It took nearly a century to figure out the basic prediction of an efficient market, from Bachelier’s random walk to the consumption Euler equation (price equals conditionally expected value, discounted by marginal utility growth). It took hard work and great insight to account for risk premiums, selection biases, reverse causality, and endogenous variables, and to develop the associated statistical procedures.

Efficient-markets empirical work doesn’t check off easy “predictions.” It typically tackles tough anomalies, each of which looks superficially like a glaring violation of efficiency, and each endorsed by a cheering crowd of rich (or perhaps lucky?) traders. It’s not obvious that what looks like an inefficiently low price is really a hidden exposure to systematic risk. It took genius to sort through the mountains of charts and graphs that computers can spit out, to see the basic clear picture.

Efficient-market predictions can be beautifully subtle and unexpected. One example: In an efficient market, expert portfolio managers should do no better than monkeys throwing darts. That’s a remarkable prediction. Experts are better than amateurs in every other field of human endeavor: Tiger Woods will beat you at golf; you should hire a good house painter and a better tax lawyer. The prediction is even more remarkable for how well it describes the world, after we do a mountain of careful empirical work.

That empirical work consists, fundamentally, of applying scientific method to financial markets. Modern medicine doesn’t ask old people for their health secrets. It does double-blind clinical trials. To this, we owe our ability to cure many diseases. Modern empirical finance doesn’t ask Warren Buffett to share his pearls of investment wisdom. We study a survivor-bias-free sample of funds sorted on some ex-ante visible characteristic, to separate skill from luck, and we correct for exposure to systematic risk. To this we owe our wisdom, and maybe, as a society, a lot of wealth as well.

This point is especially important now, in a period of great financial turbulence. It’s easy to look at the latest market gyration and opine, “Surely markets aren’t efficient.” But that’s not how we learn anything of lasting usefulness. Efficient markets taught us to evaluate theories by their rejectable predictions and by the numbers; to do real, scientific, empirical work, not to read newspapers and tell stories.

Efficient markets are also important to the world at large, in ways that I can only begin to touch on here. The assurance that market prices are in some sense basically “right” lies behind many of the enormous changes we have seen in the financial and related worlds, from index funds, which have allowed for wide sharing of the risks and rewards of the stock market, to mark-to-market accounting, quantitative portfolio evaluation and benchmarking, and modern risk management.

With 40 years’ hindsight, are markets efficient? Not always, and Gene said so in 1970. For example, prices rise on the release of inside information, so that information, though known by someone, was not reflected in the original price. More recently, I think we have seen evidence that short-sales constraints and other frictions can lead to informationally-inefficient prices.

This is great news. Only a theory that can be proved wrong has any content at all. Theories that can “explain” anything are as useless as “prices went down because the Gods are angry.”

Gene went on, arguing that no market is ever perfectly efficient, since no market is perfectly competitive and frictionless. The empirical question has always been to what degree a given phenomenon approaches an unanattainable ideal.

Still, the answer today is much closer to “yes” than to “no” in the vast majority of serious empirical investigations. It certainly is a lot closer to “yes” than anyone expected in the 1960s, or than the vast majority of practitioners believe today. There are strange fish in the water, but even the most troublesome are surprisingly small fry. And having conquered 157 anomalies with patient hard work, many of us can be excused for suspecting that just a little more work will make sense of the 158th.

However, empirical finance is no longer really devoted to “debating efficient markets,” any more than modern biology debates evolution. We have moved on to other things. I think of most current research as exploring the amazing variety and subtle economics of risk premiums – focusing on the “joint hypothesis” rather than the “informational efficiency” part of Gene’s 1970 essay.

This is also great news. Healthy fields settle debates with evidence and move on to new discoveries. But don’t conclude that efficient markets are passé. As evolution lies quietly behind the explosion in modern genetics, markets that are broadly efficient, in which prices quickly reflect information, quietly underlie all the interesting things we do today. This is the best fate any theory can aspire to.

Gene will talk about the history of efficient markets. People expect the wrong things of history as they expect overly complex “theory.” No lone genius ever thought up a “hypothesis,” went out to “test” it, and convinced the world with his 2.1 t-statistic. Theory and empirical work develop together, ideas bounce back and forth between many people, the list of salient vs. unimportant facts shifts, and evidence, argument and, alas, age gradually change people’s minds. This is how efficient markets developed too, as Gene has always graciously acknowledged. Gene’s two essays describe the ideas, but much less of this process. It was an amazing adventure, and historians of science should love this story. Ladies and Gentlemen, please welcome Gene Fama to tell us about it.


  1. Congratulations to Mr. Fama. I hope that you will be able to provide us with a personal reminiscence as he is your colleague and your father-in-law.

  2. After watching your coursera lectures, I was asking myself the other day :" Why hasn't Fama got a Nobel prize yet?" Well, glad to hear it! Congratulations!


  3. “Market efficiency means that asset prices incorporate available information about values. It does not mean that orders are efficiently processed, that prices efficiently allocate resources, or any of the other nice meanings of efficiency.”

    But don't those market prices have to retain that information for them to be truly efficient? I can say I have an energy efficient house until I open all the windows in the dead of winter.

    Meaning, I should be able to look at the market price of a particular asset and discern the financial history of the enterprise that sells / maintains the asset. Asking a lot of a snapshot aren't we?

  4. I discovered Gene Fama's work on random walks and efficient markets one summer while roaming through the library as a graduate student at Purdue in the early 1980s. It launched a lifelong fascination with testing the EMH. His work was the inspiration for a decade long project I co-directed to test whether EMH predictions hold in a small and obscure corner of the market world: private advisory services that provide crop and livestock marketing advice to farmers. We found results nearly identical to those found for mutual funds and other investments (summary here: Congrats to Gene Fama on a very deserving Nobel Prize.

    Scott Irwin
    University of Illinois

  5. I have a vague recollection of a great quote - I think from you, but I can't find it anywhere online - that whereas most economists think in graphs, Fama thinks in tables, and Hansen thinks in functional spaces (or something along those lines). Do you happen to know the source?


Comments are welcome. Keep it short, polite, and on topic.

Thanks to a few abusers I am now moderating comments. I welcome thoughtful disagreement. I will block comments with insulting or abusive language. I'm also blocking totally inane comments. Try to make some sense. I am much more likely to allow critical comments if you have the honesty and courage to use your real name.