News stories published mostly by small- to medium-sized outlets boosted Twitter conversations about those topics by about 63% across the political spectrum, suggests a five-year experiment released on Thursday.

Twitter has 328 million active users — journalists and news hounds, politicians and public agencies, activists and Russian trolls — a real-time cacophony that has become the water cooler of the internet.

The platform has also become a laboratory for social scientists trying to tap into the national conversation. In the new study, published in the journal Science, researchers enlisted 48 news outlets to participate in a five-year experiment in which they agreed, on certain weeks, to publish stories about topics chosen by the scientists, in a bid to understand the impact of their work.

As it turned out, the impact was significant: The stories were not only talked about, but shifted people’s opinions ever so slightly toward the political outlook of the news outlets, the study found.

“What this tells us is that journalists bear considerable responsibility for a crucial part of American democracy,” study lead author Gary King of Harvard told BuzzFeed News. “This is not just another job. It really matters.”

Although it’s common sense that the news has some effect on society, measuring its precise impact on political chatter has been tough, King said. “This was much bigger than we had realized or previous scholars had understood.”

The participating media ranged from general-audience outlets like The Huffington Post to niche publications such as Yes! Magazine, Feministing, and Alternet. Most skew liberal, according to the researchers.

On 35 separate weeks, several outlets would collaborate with each other on a story about one of the selected topics, such as abortion, immigration, jobs, and climate change, as well as publishing their own articles. Then the researchers measured all of the tweets that linked to or mentioned the articles, whether favorably or not.

All of the stories were real news the outlets produced and promoted in normal fashion. Apart from telling the outlets which topics they were focusing on in a given week, the study team did not influence what, or how, the news was reported. (BuzzFeed News was not part of the experiment.)

King said most of the study team’s time was was spent negotiating cooperation with the news outlets. "I learned every time they started to talk about 'journalistic integrity' I had crossed a line, and needed to start the conversation over," he said.

To make everybody happy, the researchers eventually followed the collaborative model of the 2016 “Panama Papers” investigations, in which a consortium parceled out documents detailing dodgy offshore investments to various outlets, allowing them to freely pick ones for stories, an effort that won the Pulitzer Prize in April. The funders of King’s study, The Media Consortium, a “progressive” media association, also paid outlets for their participation.