…14.6%, 4.6%, and -0.3%. How does a three-year number change so fast, and does this mean the fund went from great to awful?

Well, the manager didn't change. The fund's strategy didn't change. The only thing that changed was the date.

While the intentions are good, and consistency in the industry is necessary, the standard performance measures don't really give you insight into a fund's real performance picture.

That's why I developed my proprietary rolling returns analysis.

Instead of focusing on a single 12-month, three-year, and five-year period, my rolling returns measure average performance over scores of 12-month, three-year and five-year periods.

In a decade of returns, I analyze more than 80 three-year periods and more than 50 five-year periods–January 2005 to December 2005, February 2005 to January 2006, and so on. Each of these periods is a "snapshot" of a fund's real-world performance.

Then I use my rolling returns formula to crunch the numbers and reveal the fund's actual average performance. The result is a more accurate, complete picture of how a fund actually performs. Rather than compare a fund's single performance period to another, I can compare their long-haul performance.

It turns out that there are plenty of Vanguard funds, for instance, that have put the 500 Index fund to shame over any number of periods. Using the industry's method you'll invariably find funds that look great one year, but turn out to be losers over the long haul.

You won't get these numbers from Vanguard, the Wall Street Journal, or any mutual fund. Dan Wiener is the only one who takes the time to both calculate rolling returns and explain them to his readers and clients. You can find the rolling returns and other proprietary measures of all of Vanguard's funds in Dan's annual Independent Guide to the Vanguard Funds. With more than 100 funds profiled in a quick-reading fashion, no Vanguard investor should be without this resource. And you can get the Guide as a free gift when you subscribe to The Independent Adviser for Vanguard Investors. Click here now to learn more about this special offer.