The company that measures television viewership will soon begin counting people who watch programming through broadband instead of a traditional broadcast or cable hook-up.

The move announced Thursday by Nielsen is a significant step toward recognizing a world where the definition of TV viewing is swiftly changing. For many years, roughly 99 percent of homes in the U.S. had televisions that received service through broadcast, cable or .

Now the number of homes without such service is 4.2 percent—and growing each year. Most of those homes have TVs, however, and their owners watch programming through or services like and Amazon. Starting September, Nielsen will begin tracking the habits of these homes.