Forbes.com is at the center of a hubbub about audience measurement, highlighting the differences between self-reported data and those reported by third-party, research firms.

Forbes.com - which has been thriving online even as its print counterpart, Forbes magazine, has undergone a decline in advertising - claims a worldwide audience of nearly 15.3 million, using February data from comScore Media Metrixwrites the New York Times (via MediaBuyerPlanner). However, comScore itself has since revised that number downward to fewer than 13.2 million, saying that visits to Forbes.com have tumbled since February, .

Forbes's own ads claim that "more people get their business news from Forbes.com than any other source in the world," but in July the website drew just 7.3 million unique visitors worldwide, putting the site slightly below Dow Jones, CNNMoney.com and sites affiliated with Reuters. Each of those competitors had some 7.6 million visitors that month, according to comScore.

James Spanfeller, chief executive of Forbes.com and chairman of the Interactive Advertising Bureau, says comScore's latest figures clash with his own internal reporting, which still shows about 15 million visitors per month. He also points out that many of the competitor sites's statistics have been revised downward by comScore.

Nielsen/NetRatings's latest numbers, based on visitors from the U.S., also place Forbes.com below Dow Jones and CNNMoney, and Forbes.com's statement of dominance in the marketplace is one that irritates competitors, particularly as Forbes.com brought in nearly $55 million in revenue in 2005, beating out all other business publications, including the Wall Street Journal, BusinessWeek and the business pages of the New York Times.

While differences in reporting are nothing new in the online ad industry, particularly between websites and third-party web-tracking companies, the kafuffle reported by the Times may bring into the spotlight once again the need for a generally accepted online measurement system.

The proliferation of differing web traffic statistics is confusing to even the most savvy marketer. It is an issue that needs to be addressed, according to Spanfeller.