Forget buzzy new shows like “The Queen’s Gambit” and “Normal People.” The three series that people spent the most time watching on the major streaming platforms in the United States in 2020 all premiered on network TV more than a decade and a half ago, the research firm Nielsen found.

“The Office,” “Grey’s Anatomy” and “Criminal Minds,” network shows with hundreds of back episodes available to stream on Netflix and other services, each accounted for more viewing time than any other show or movie, new or old, Nielsen said on Tuesday.

The most-watched movie of the year was “Frozen II,” one of several movies that attracted viewers to Disney+ in droves. The most-watched series that premiered on a streaming service was the Netflix crime drama “Ozark,” according to Nielsen.

The list seemed to confirm earlier findings that Americans favored comfort and escapist entertainment, in addition to news, as the nation confronted a public health emergency, massive social unrest and a searing presidential election.

This is the first time that Nielsen — the 98-year old company that provides ratings information for broadcast and cable networks — has ranked the most-streamed shows of the year. It started releasing weekly most-streamed lists in 2020.

The Nielsen list offers some insight into how people consume shows on streaming services, a question that third-party firms have urgently been trying to figure out a reliable way to answer.

There are some caveats, however. Nielsen’s survey only measures households in the United States, and a view only counts if a show or movie is watched on a TV. If a viewer in the survey watches a show or movie solely on their phone, tablet or computer, Nielsen cannot measure it. Nielsen reported viewership for Netflix, Disney+, Hulu and Amazon but has not yet released figures for Apple TV+, HBO Max or Peacock.

That’s significant because, starting this year, “The Office” is on Peacock, not Netflix. HBO Max has the rights to another enduring sitcom, “Friends.”

“The Office,” “Grey’s 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. (“Grey’s 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 what’s happening to Dwight Schrute.”

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

The Netflix documentary “Tiger King” was the only show in Nielsen’s 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 Nielsen’s 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 Rhimes’s new drama, “Bridgerton,” was the service’s fifth most-watched original series, with viewership in the same league as “Tiger King” and “The Queen’s Gambit.”)

Though Netflix dominated the acquired series and original series Nielsen lists, Disney+ overwhelmed its streaming rivals among movies.

Of the top 10 movies, seven belonged to Disney+ and three were from Netflix. Eight of the 10 were animated, with the exceptions being “Hamilton” on Disney+ and “Spenser Confidential,” a Netflix action film starring Mark Wahlberg.

While the list included newer movies like “Frozen II” and Pixar’s “Onward,” older films like “Moana” and “Zootopia” were also in the top 10. For a list that’s adding up total minutes viewed, it’s not difficult to discern why.

“Kids are watching those movies over and over and over again,” Mr. Fuhrer said.