Nielsen Media Research may count viewers who watch online through the Comcast and Time Warner “TV Everywhere” services in a show’s overall ratings, but not until 2011, says B&C.

Nielsen told clients in a letter Tuesday that such a step will come only after serious evaluation.

According to B&C, Sara Erichson, president of Nielsen’s Media Client Services for North America, wrote: "Given that more than $70 billion of television advertising is bought and sold using Nielsen ratings, we are careful not to take any actions that would dilute the reliability of the core television ratings data. Consequently, we are undertaking an extensive evaluation program before fully integrating television and Internet measurement."

Nielsen in under some pressure to create a single source measurement system. A number of Nielsen clients have formed the Coalition for Innovative Media Measurement, which plans to publicly announce its plans some time this month.

–Elizabeth Jensen and Chuck Ross