The Office, Greys Anatomy and Criminal Minds represent three genres that have been mainstays in American entertainment workplace comedies, and medical and crime dramas. They also feature a combined library of 830 episodes, which significantly boosted them in the Nielsen lists, which ranked shows based on total minutes watched. (Greys Anatomy is still running on ABC and is in its 17th season.)

These programs disproportionately benefited from the fact that they just had a lot of real estate, they have a lot of episodes for people to watch, said Brian Fuhrer, a senior vice president at Nielsen. And what they also do is they provide a sense of normalcy. They can go back and find out whats happening to Dwight Schrute.

Among original series, the only non-Netflix show in Nielsens top 10 list was the popular Disney+ Star Wars spinoff, The Mandalorian.

The Netflix documentary Tiger King was the only show in Nielsens original series list to have as few as eight episodes. It premiered on March 20, just as stay-at-home orders were being issued throughout the country, and a week before the third season of Ozark became available on Netflix.

They both hit right in the heart of the pandemic when people were locked at home, with not much to do, Mr. Fuhrer said. They were both viewed extremely heavily.

While broadcast and cable networks rely on Nielsen to inform them of what people are watching, all of the streaming companies have their own internal metrics. None of them have publicly endorsed Nielsens methodologies, nor do they need those figures to determine which shows to promote or cancel.

For more than a year, Netflix has been publicly disclosing worldwide figures for original shows, providing some sense of what people are watching. But its list comes with significant caveats. Netflix counts viewers that watch as little as two minutes of a program, and the service is extremely selective in what shows and movies it discloses figures for. (For instance, Netflix recently said Shonda Rhimess new drama, Bridgerton, was the services fifth most-watched original series, with viewership in the same league as Tiger King and The Queens Gambit.)

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The Office and Greys Anatomy Top List of 2020's Most-Streamed Shows - The New York Times