Among the publishers now being rated via the Quantcast service, are popular news aggregation service Digg.com, tech journal publisher IDG's Web sites, and burgeoning youth lifestyle social network Going.com, which are prime examples of the kind of catch-22 faced by small, but fast-growing publishers who cannot get audience estimates from the big panel-based measurement services.

Going.com, a social network focusing on the twentysomething, bar-hopping scene, for example, is big in big metropolitan areas like New York, Los Angeles, Chicago, Boston and San Francisco, but does not have the kind of national coverage yet that would qualify it for comScore's or Nielsen's panels.

"We are relying on Quantcast data to better establish our value proposition to key advertising prospects," conceded Evan Schumacher, CEO of Going.com. "Rapidly growing sites like ours can be under-reported or misrepresented by panel-based services, and we've found that agencies trust Quantcast data as part of their evaluation process.

To illustrate the really long tail aspect of the online audience ratings dilemma, Quantcast marketing chief Adam Gerber notes that popular blogging platform provider WordPress is currently looked as a single publisher by the panel-based ratings services, but it actually powers 1.8 million individual blogs that would otherwise go unmeasured if it weren't for the Quantcast program. "We provide audience profiles for 60,000 individual vanity blogs powered by WordPress," Gerber noted.

Quantcast's quantified program also is gaining traction among some big buyers of online media - agencies that buy niche sites that are relevant for specific brands, but which remain unmeasured by the panel measurement services. For client Toyota, for example, Saatchi & Saatchi LA utilizes Quantcast to evaluate smaller automotive related sites.

Some agencies have even begun tagging their own client's brands sites to ensure they are rated by Quantcast's quantified program - such as Goodby, Silverstein & Partners is doing for client Sprint - in order to understand and evaluate the traffic and audience profiles they are generating.

Quantcast's quantified program is actually one half of a hybrid ratings process developed by Quantcast, and allows the firm to proactively measure the audiences of specific Web sites on a direct basis utilizing the Internet population as an actual census. The other half is a purely passive, census-based measurement of all Web publishers, regardless of whether they tag for measurement by Quantcast.

The hybrid process is becoming increasingly popular among online audience researchers, and during the Interactive Advertising Bureau's recent online audience metrics forum in New York, Nielsen Online research chief Manish Bhatia unveiled a new census-based system - Nielsen Online's "Video Census" - that is testing a similar hybrid process that measures both tagged sites proactively, and the untagged universe passively.

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