Sep 15, 2009
How useful was Monte Carlo-type analysis in preparing for the recent downturn in the economy and stock market? Is there an alternative approach that investors should consider in an effort to address the uncertainty of future returns?

EFF: Monte Carlo analysis is overkill here. All one really needs is good historical perspective on the volatility of volatility. Our white paper, "How Unusual Was the Stock Market of 2008?", is a good start. 

KRF: Monte Carlo analysis is often worse than overkill because it gives many users a false sense of precision. If used right, it can provide some perspective about the payoff on a long-term investment. Investors who do Monte Carlo simulations, however, often assume returns are drawn from a normal distribution with a constant volatility. In fact, a normal distribution produces far fewer extreme returns than we see in the market. Moreover, it is easy to forget that the inputs for the analysis - the estimated expected returns, variances, and covariances - are almost certainly grossly imprecise.

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.