For one week back in 2012, Facebook scientists altered what appeared on the News Feed of more than 600,000 users. One group got mostly positive items; the other got mostly negative items.

Scientists then monitored the posts of those people and found that they were more negative if they received the negative News Feed and more positive if they received positive items.

As the New Scientist reports, the research means "emotional contagion" can happen online, not just face to face. The magazine adds:

"The effect was significant, though modest.

"Ke Xu of Beihang University in Beijing has studied emotional contagion on Chinese social networks. He says [Facebook's Adam] Kramer's work shows that we don't need to interact in person to influence someone's feelings."

The findings are published in the current edition of the Proceedings of the National Academy of Sciences.

If you're wondering: Yes, this kind of experiment is in line with Facebook's terms of use. The Verge reports:

"When users sign up for Facebook, they agree that their information may be used 'for internal operations, including troubleshooting, data analysis, testing, research and service improvement.' While there's nothing in the policy about altering products like the News Feed, it's unlikely Facebook stepped outside the bounds of the Terms of Use in conducting the experiment. Still, for users confused by the whims of the News Feed, the experiment stands as a reminder: there may be more than just metrics determining which posts make it onto your feed."

Copyright 2021 NPR. To see more, visit https://www.npr.org.