How much of what you see on social media comes from sources that repeatedly post falsehoods? And if that content quietly vanished from your feed, would you believe anything different months later?

A new study published today in Science Advances offers the most rigorous answers yet. It comes from a collaboration between Meta and academic researchers who studied the 2020 United States election. It was run from inside the machine – on the live feeds of Facebook and Instagram.

The answers sound reassuring: exposure to lies was rare for most users, and removing them did not measurably shift anyone’s beliefs. But, as a researcher who studies how misinformation permeates these platforms, I think the fine print matters more than the headline.

Our political attitudes are shaped by television, talk radio, politicians, family and friends, so isolating social media’s contribution is particularly difficult. People also self-select: those drawn to fringe content surround themselves with others like them in tight clusters, so observation alone can easily miss them, and proves little.

The clean way through is a randomised experiment inside the platform, and only the platform can run one. That is what makes this study valuable.

The team of researchers, led by Olivier Bergeron-Boutin from the University of California, Berkeley, first measured how much content – across 231 million adult US Facebook accounts and 200 million Instagram accounts – came from “untrustworthy sources”. These included........

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