Harry Markowitz

I would never be 100 percent in stocks or 100 percent in bonds or cash.

During the 1950s, I decided, as did many others, that many practical problems were beyond analytic solution and that simulation techniques were required. At RAND, I participated in the building of large logistics simulation models; at General Electric, I helped build models of manufacturing plants.

I was born in Chicago in 1927, the only child of Morris and Mildred Markowitz, who owned a small grocery store. We lived in a nice apartment, always had enough to eat, and I had my own room. I never was aware of the Great Depression.

Becoming an economist was not a childhood dream of mine.

In 1989, I was awarded the Von Neumann Prize in Operations Research Theory by the Operations Research Society of America and The Institute of Management Sciences. They cited my works in the areas of portfolio theory, sparse matrix techniques and the SIMSCRIPT programming language.

Diversifying sufficiently among uncorrelated risks can reduce portfolio risk toward zero. But financial engineers should know that's not true of a portfolio of correlated risks.

Portfolio theory, as used by most financial planners, recommends that you diversify with a balance of stocks and bonds and cash that's suitable to your risk tolerance.

The chief problem with the individual investor: He or she typically buys when the market is high and thinks it's going to go up, and sells when the market is low and thinks it's going to go down.

If the investor doesn't have enough time and skill to investigate individual stocks or enough money to diversify a portfolio, the right thing to do is to invest in exchange-traded funds that give you exposure to asset classes. It does make sense for the individual investor to think in terms of holding individual asset classes.