This interview of Eugene Fama, who is commonly referred to as the father of the Efficient Market Hypothesis (”EMH”), was conducted in August 2009 by Dimensional Fund Advisors.
A few highlights:
Responding to critics that the recent volatility has ”killed” the EMH:
“The market can only know what’s knowable. It can’t resolve uncertainties that are unresolvable. So when there’s a large amount of economic uncertainty out there, there’s going to be a large amount of volatility in prices. As far as I’m concerned that’s exactly what we’d expect an efficient market to look like.”
Paraphrasing other interesting comments:
Most behavioral finance advocates like to point out inefficiencies, but usually conclude that it’s too impractical to take advantage of these inefficiencies and therefore you’re better off to do your risk-return tradeoff. In other words they conclude that you’re better off to presume the EMH is an accurate description of the way markets work.
The top insiders do better trading on their own company’s stock but interestingly only by about 1%.
The most potent challenge to the EMH is evidence of momentum in stocks that can’t be easily explained. Secondly, movements due to earnings announcements tend to persist longer that expected. Those are the two biggest challenges. Remember, EMH is a model, not truth. It’s a simplification of the world that does a good job on almost everything, but a few things it doesn’t do a good job on, e.g. insider trading, momentum, and movement from earnings announcement.
The EMH is not a perfect explanation of everything that happens in the market, but it is the best working proposition for use by investors. Most investors should presume that the only way to reliably affect the expected return from their portfolio is by varying the level of risk they’re prepared to take. Nothing in the last 12 months has altered that. Some people are claiming the market isn’t efficient, but they aren’t claiming there are easy profit opportunities out there. It’s one or the other.
Whether you agree or disagree with Fama and EMH, this is a must-see interview in light of the recent volatility in the debate about EMH (ha ha).