In April 2018, Mark Zuckerberg, Facebook’s chief executive, told Congress about an ambitious plan to share huge amounts of posts, links and other user data with researchers around the world so that they could study and flag disinformation on the site.

“Our goal is to focus on both providing ideas for preventing interference in 2018 and beyond, and also for holding us accountable,” Mr. Zuckerberg told lawmakers questioning him about Russian interference on the site in the 2016 presidential election. He said he hoped “the first results” would come by the end of that year.

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“We and Facebook have learned how difficult it is to make” a database that was not just privacy-protected but at a “grand scale,” said Nate Persily, a Stanford law professor and co-founder of Social Science One.