From an interview of MIT's Andrew Lo:
Q: Many people believe that the financial crisis revealed major shortcomings in the discipline of economics, and one of the goals of your book is to consider what economic theory tells us about the links between finance and the rest of the economy. Do you feel that economists understand enough about the nature of financial instability or liquidity crises?
A: I think that the financial crisis was an important wake-up call to all economists that we need to change the way we approach our discipline. While economics has made great strides in modeling liquidity risk, financial contagion, and market bubbles and crashes, we haven't done a very good job of integrating these models into broader macroeconomic policy tools. That's the focus of a lot of recent activity in macro and financial economics and the hope is that we'll be able to do better in the near future.
Q: Let me continue briefly on this thread. One topic has been particularly controversial concerns the efficient-market hypothesis (EMH). Burton Malkiel discusses the issue in his chapter in Rethinking the Financial Crisis, but I wanted to ask your opinion of this idea that EMH fed a hands-off regulatory approach that ignored concerns about faulty asset pricing.
A: There's no doubt that EMH and its macroeconomic cousin, Rational Expectations, played a significant role in how regulators approached their responsibilities. However, we should keep in mind that market efficiency isn't wrong; it's just incomplete. Market participants do behave rationally under normal economic conditions, hence the current regulatory framework does serve a useful purpose during these periods. But during periods of extreme growth and decline, human behavior is not the same, and much of economic theory and regulatory policy does not yet reflect this new perspective of "Adaptive Markets."