Nielsen’s local and national TV ratings will begin to include set-top box data from the nation’s No. 1 TV distributor, AT&T, this year as a result of a multi-year agreement the companies announced this morning.

The information, they say, will be “anonymized” –industry-speak that means it will identify characteristics of viewers, but not their identities.

By adding information about DirecTV and U-Verse viewing, Nielsen will be able to offer “enriched, electronic measurement in all 210 local TV markets,” the announcement says. It will be “incorporated with data from other data providers to complement Nielsen’s national and local suite of products, such as Nielsen Scarborough, NLTV and Nielsen N-Score.”

Set-top box data is especially helpful in small markets where the sample sizes for Nielsen’s surveys often are too small to give advertisers a clear sense of what niches of viewers watch.

The integration of set-top box data with viewing information from surveys “is at the center of our TV measurement strategy to enhance how TV viewing is measured,” Nielsen Product Leadership President Megan Clarken says. It helps the company to offer clients “comprehensive, reliable and in-depth measurement of how people consume content in today’s changing media landscape.”

The announcement comes as Nielsen plans to roll out its Total Audience Ratings, which will include digital and out of home viewing measurements along with traditional, in home viewing.

In April, Nielsen reached a similar deal to use set-top box data from DirecTV’s closest competitor: Dish Network.

Although Nielsen has a firm grip on the national ratings business, ComScore, which bought Rentrak early last year, has cited its access to set-top box data as a competitive advantage for broadcasters and advertisers looking to improve local sales.