• Fortune, Wednesday, August 22, 2007 10:45 AM

The Internet is advertising's most measurable medium, but despite available research, Web data isn't necessarily accurate, posing a massive problem for advertisers. You've seen it before: depending on whom you ask, comScore or Nielsen/NetRatings, Yahoo either had 133 million unique visitors in June or 108 million. That's not a small difference.

So which do you believe? Both companies stand by their research methods. Understanding advertisers' woes, the IAB recently called for a public audit and accreditation of their research. "It's a really rough science," said company CEO Randall Rothenberg. But what will that do? How do you audit a business as tricky as Web measurement, anyways? Counting page views and unique visitors is hard enough, especially when you consider heavier consumption on portable devices and handsets.

The new question is whether page views are an accurate representation of a site's worth. After all, not all page views are created equal, says comScore CEO Magid Abraham--whose company yesterday announced it would measure things like widgets and video downloads and expand its search measurement to include eBay and Amazon. Nielsen/NetRatings several weeks ago said it was changing its de facto traffic measurement to time spent on a given Web property. Nevertheless, they embrace the public audit.

Read the whole story at Fortune »