One of the most common mistakes made in the retirement investing world, particularly among 401(k) participants, is over-concentration in an employer's stock. In an analysis of more than 100,000 401(k) participants from companies offering stock in their 401(k) plan, more than 54 percent of employees had stock concentration levels that were greater than 20 percent of their total account, an amount that is enough to significantly decrease their median forecasts. In fact, loading up on your employer stock is even worse than loading up on a random individual security. Why? Because chances are your job (and hence your future income) is likely to be highly correlated with how the company stock performs. If bad things happen to the industry or the stock of your employer, you are likely not only to lose your money on the investment, but possibly your job as well. As the unhappy former employees of Enron can attest, this double whammy effect can be devastating, particularly if you are nearing retirement. This implies that you should be even less likely to want to hold the stock of your employer than you would be to hold the stock of a random company. Unfortunately, surveys suggest that many employees do exactly the opposite, loading up on their employer stock in their retirement plan.

People often confuse a good company with a good stock. Your company may be the most amazing, creative, world-dominating, run-by-geniuses firm around, but that does not mean that the stock is undervalued. Chances are, all that good stuff about the company is already factored into its price by the market. To determine that something is undervalued, you have to have information about the future prospects of the firm that are not understood by the market. If it is public, you can bet that the markets have already digested the information. If the new information is private, you are prohibited by law from trading on it (this is called insider information). Never make the mistake of assuming that a great company implies a great stock.

Sometimes the impact of stock volatility can be counterintuitive. Consider an investor at the beginning of January in 1997. Let's say this investor consulted a magical genie and was offered a stock pick that would return an average of 37 percent per year for the next six years guaranteed. The genie states that there would be many bumps along the road, but the investment was guaranteed to have average annual returns of 37 percent. The investor does a quick calculation in his head and determines that if he invests $100,000 in the stock and gets an average annual return of 37 percent, then he stands to make about $560,000 over the next six years. Not a bad deal, right? Sure, there will be some volatility, but those guaranteed average annual returns look pretty good. The investor thanks the genie and promptly goes off to invest his $100,000 in the recommended stock.

Fast forward six years later to December 31, 2002. As promised by the genie, the stock pick has achieved annual returns of 37 percent over the six-year period. But the investor is astonished to see that his account balance is only $80,130. He actually lost 20 percent of his money! What the heck happened?

The stock in this example (JDS Uniphase Corp.) actually did have average annual returns of 37 percent over the period January 1, 1997, through December 31, 2002. But the growth rate (which takes into account the impact of the volatility) was an anemic -3.6 percent per year. The average return was pretty good, but the volatility of the stock's performance killed the growth rate.

The stock had extraordinary performance in the period leading up to early 2000, but this was matched by equally poor performance in 2001 and 2002. The result was that average returns were strongly positive for the six year period, but the overall cumulative performance was poor. This is an extreme example, but clearly demonstrates the danger of focusing too much attention on average returns without considering the impact of volatility. Remember that volatility matters a lot in accumulating wealth over time.

The above is an excerpt from the book The Intelligent Portfolio by Christopher L. Jones Published by John Wiley & Sons, Inc.; May 2008;$27.95US/$30.99CAN; 978-0-470-22804-3 Copyright © 2008 Christopher L. Jones

Author Bio

Christopher L. Jones is Chief Investment Officer and Executive Vice President of Investment Management for Financial Engines. Working closely with founder William F. Sharpe, Jones built and led the team of experts in finance, economics, and mathematics that developed the financial methodology for Financial Engines' personalized investment advice and management services. Jones has led the investment management function at Financial Engines for more than a decade. He holds an MS in business technology, an MS in engineering-economic systems, and a BA in quantitative economics, all from Stanford University.