Launched in September, Quantcast's Quantified Publisher program allows any size publisher to participate for free by tagging pages. The company plans to eventually make its money by matching advertisers with target audiences, in effect creating an audience search engine, said co-founder and CEO Konrad Feldman.

Among the higher-profile sites of the thousands using the free service at www.quantcast.com are Fox.com, Facebook.com, Answers.com, TheNation.com, MIT, Gawker.com, Weather Underground, The HuffingtonPost.com, and Nerve.com.

"As the IAB recognizes, panel-based research has passed the breaking point for sizing Internet audiences," Feldman said. "Panels have value, but we use a range of complementary approaches."

Publishers using Quantcast, he said, sometimes find results that confirm panel measurements, and sometimes do not.

"With our recent shift to a social news focus, we wanted to see exactly how our community is developing," said Tom Drapeau, director of Netscape, a new participant. "Until now, all available analytics have either understated or overstated our audience size."

Online advertising spending exceeded $16 billion last year by IAB estimates, but it was concentrated among the portals. Niche sites often go uncounted or undercounted by panels.

"It's hard to spend significant money online. The only way now is through the portals. We believe the lack of accurate data is holding back the industry," Feldman added.

Interpreting Web traffic data with state-of-the-art statistical models, the Quantified Publisher program aims to level the playing field by giving Web publishers of all sizes accurate traffic, demographic and lifestyle data on their audiences.

"Even though we have server logs and analytics about who visits the blogs on WordPress.com, it wasn't until we started using Quantcast that we got a sense of 'who' those people were," said Matt Mullenweg, founder of WordPress.

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