Mar 18, 2009
Is diversification working today, when we need it most?

EFF/KRF: When overall market volatility increases, idiosyncratic (security-specific) volatility also tends to increase. For example, market volatility is currently quite high, and the dispersion of the cross section of stock returns (which is idiosyncratic volatility) is also unusually high. Diversification has no effect on the volatility of the overall market, but it reduces the effect of idiosyncratic volatility on a portfolio's return. To put it differently, active investment is a riskier strategy when volatility is high because active portfolios are, almost by definition, poorly diversified.

In short, diversification is now more important than usual.

Eugene F. Fama
The Robert R. McCormick Distinguished Service Professor of Finance at the University of Chicago Booth School of Business
Kenneth R. French
The Roth Family Distinguished Professor of Finance at the Tuck School of Business at Dartmouth College
This information is distributed for educational purposes and should not be considered investment advice or an offer of any security for sale. This article contains the opinions of the author but not necessarily Dimensional Fund Advisors and does not represent a recommendation of any particular security, strategy or investment product. Dimensional Fund Advisors is an investment advisor registered with the Securities and Exchange Commission. Information contained herein has been obtained from sources believed to be reliable, but is not guaranteed. Past performance is not indicative of future results and no representation is made that the stated results will be replicated.

Eugene Fama and Ken French are members of the Board of Directors of the general partner of, and provide consulting services to Dimensional Fund Advisors LP.