In a bid to help marketers measure audiences for ads across TV, online and (eventually) mobile platforms by a common metric, Nielsen unveiled a new system Monday—to be launched commercially next year—that will provide, for the first time, TV-type ratings for Internet display and video spots on sites like Facebook and Yahoo!

The new system, called Nielsen Online Campaign Ratings, presented during Advertising Week, will enable Nielsen to combine data from its own online rating panels with data from third-party contributors like Facebook to more precisely measure how many people—by gender, age, reach and frequency--are viewing ads online. The data is combined through the use of tags known as pixels that alert Nielsen each time a particular ad is displayed in a browser.

Media, marketing and agency executives heralded the service as a breakthrough. "Impressions and clicks aren't doing anybody a favor" when it comes to understanding the effectiveness of online advertising, said Mike Murphy, chief revenue officer at Facebook.

A big part of the problem with online measurement, said Kate Sirkin, global research director at Starcom MediaVest Group, is that numerous companies using various methodologies are measuring the space. "Planning, buying and posting are all based on different metrics," she said. "It's too hard to make comparisons."

Suzy Deering, executive director of media and sponsorships at Verizon Wireless, said the new system is a "big step in the right direction." She said she couldn't remember the last time she watched TV without simultaneously using another device, either computer or mobile. She said many viewers are adopting similar habits and that Nielsen's new system will help marketers better understand that evolving behavior.

Privacy is a sensitive issue with the new technique, and Nielsen stressed that it does not track consumers from one Web site to another.

Nielsen will test the service in the fourth quarter with several partners, including Facebook, Procter & Gamble, Verizon Wireless and SMG.

Others also support the initiative, such as Omnicom Media Group. However, OMG's U.S. director of media research, Michael Atkin, said the company is "taking a wait-and-see attitude and is assessing on a client-per-client basis as the effort evolves."

Watch the announcement: