Nielsen's new cross-platform service brings together two worlds and gives advertisers a better sense of who's watching. - 

Jeremy Hobson: When companies advertise on TV they can find out what kind of people are watching their ads. When they advertise on the Internet, they have even better technology to see who they're reaching. But what if they want to find out if the same person is viewing the ads online and on TV?

Well the ratings company Nielsen is launching a new service that'll do just that. Jennifer Collins reports.

Jennifer Collins: Online and TV ratings have long been available separately. But Tim Calkins, a marketing professor at Northwestern University, says advertisers want to know where their ad campaigns overlap. Take Dannon yogurt, for instance.

Tim Calkins: You know their challenge is they're trying to reach a lot of people very quickly because they're in a big fight with Chobani and a lot of the upstart Greek yogurts.

Nielsen's new service could help Dannon determine if the same people who see its ads online see them on TV, or if the campaign is, in fact, expanding Dannon's reach. Nielsen says it's tracking online and TV viewership in 15,000 households.

Mark Lieberman is the CEO of TRA, another media tracking firm.

Mark Lieberman: This is definitely a step in the right direction. There's no doubt it’s something the industry wants and needs.

He says Nielsen's service could help advertisers figure out how to divide up their marketing budgets to reach the biggest audience.

I'm Jennifer Collins for Marketplace.