The Upside of Risk

If you want higher returns, you have to accept the thrills and spills that accompany them.

Investors this summer got a rude taste of something many of them had forgotten: volatility. Knowing what a stock (or any other investment) returns over time is not enough. You need to know how consistent those returns will be. Think of a baseball player who hits .198 one year, .376 the next and .280 the next. Computing his three-year batting average of .285 tells you little about the volatile, inconsistent nature of his hitting.

Measuring the jolts. A common measure of stock volatility -- that is, the extremes of the market's ups and downs -- is standard deviation, an expression of how much prices vary from their own average movement. History shows that the standard deviation of the U.S. market as a whole has been about 20 percentage points. Because stocks (using Standard & Poor's 500-stock index as a benchmark) have returned an annualized average of about 10%, two-thirds of the time we can expect S&P returns to range between -10% and +30%. Lately, however, returns have fallen into a much narrower range. For the four years starting in 2003, the S&P returned 29%, 11%, 5% and 16%. For the three years that ended last June 30, the standard deviation of the S&P was a mere 7. No wonder investors had gotten used to smooth sailing.

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James K. Glassman
Contributing Columnist, Kiplinger's Personal Finance
James K. Glassman is a visiting fellow at the American Enterprise Institute. His most recent book is Safety Net: The Strategy for De-Risking Your Investments in a Time of Turbulence.