Comcast will sell access to its trove of data on how Americans watch TV to Comscore, a media analytics firm that measures TV audiences, the companies said Friday.

The Philadelphia cable giant will license viewership data from customers’ set-top boxes, which Comscore will use to improve its measurements of TV ratings. The audience measurements are used by buyers and sellers of advertisements. At least $70 billion was spent on TV advertisements in 2019, according to market researcher eMarketer.

It’s a rare deal for Comcast, the company says. The Philadelphia media giant didn’t provide this type of consumer data to anyone in the industry until 2017, when it reached a similar deal with Nielsen, even as other pay TV providers and online streaming services made such data available. In 2015, Comcast turned down a $100 million offer from Nielsen for an exclusive license to the data, according to the Wall Street Journal.

Neither Comcast nor Comscore disclosed financial terms of the agreement.

Comcast said the data is de-identified, meaning it does not include the names, addresses, or other personal information of customers. The data doesn’t identify specific set-top boxes either, so viewing information cannot be traced back to a user or household.

Comcast, the nation’s largest cable TV operator, had been a holdout in terms of sharing such viewership data with audience measurement firms. Comscore said it has had access to such data from other pay TV companies for a decade, starting with Dish.

Comscore CEO Bill Livek said the Comcast deal will strengthen the ratings firm’s measurement of television households across the country. Comscore already had access to data from Dish, DirecTV, Charter, and Cox.

“It is a major step in our ongoing journey toward more precise measurement, helping us develop better products to serve our customers and drive revenue growth in the coming years," Livek said in a statement.

The deal comes a few days after Comcast’s NBCUniversal announced that its advertisers can now buy ads on different video services, target precise audiences, and better measure how ads perform in an all-in-one technology system. NBCUniversal is preparing to launch a video streaming service this spring, called Peacock.

Spending on such advertising — industry insiders call it connected TV ads — is expected to reach $14 billion by 2023 according to eMarketer. That market is increasingly important for companies like Comcast as traditional TV advertising market continues to shrink — it is expected to drop to more than $68 billion in 2023.