Counterfeit and pirated goods are a big problem for global business, costing hundreds of billions of dollars, according to manufacturers and trade groups. But their estimates tell more about how difficult it is to assign a value to lost sales than about the actual size of the counterfeiting problem.

Washington business groups such as the U.S. Chamber of Commerce and the International AntiCounterfeiting Coalition calculate that global counterfeit sales equal $600 billion to $650 billion a year -- numbers parroted in news releases by companies claiming to fight piracy. They build on the often-cited claim that counterfeit goods represent 5% to 7% of all world trade. That claim got its official launch in a 1997 report by the International Chamber of Commerce, which cited these percentages as only a "general assumption."

"It is virtually impossible to find accurate statistics to substantiate these perceptions" that counterfeiting is on the rise, the ICC author wrote.

The barriers to accurate data on piracy are clear: It's a shadowy business run by criminals.

Yet from these shaky foundations, a new gospel was born: 5% to 7% became the ubiquitous estimate. It was used in a 1998 report by the Organization for Economic Cooperation and Development and is often attributed to that group -- "unfortunately," OECD Deputy Director for Science, Technology and Industry John Dryden wrote earlier this year, because the number is based on methodology that is "not clear."