Many Facebook users are having very emotional responses after learning that the social media company manipulated the news feeds of more than a half a million users as part of a psychological study.

For one week in January of 2012, Facebook randomly selected users to change how many positive and negative posts they saw, to see how emotions can be spread on social media.

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The results were pubished this month in the academic journal Proceedings of the National Academy of Science. Researchers found users who saw more negative content were more likely to create their own negative posts. Those shown more positive content were more likely to create positive posts.

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“The goal of all of our research at Facebook is to learn how to provide a better service,” said Facebook Data Scientist Adam Kramer in a post on the site. “Having written and designed this experiment myself, I can tell you that our goal was never to upset anyone.”

Facebook already uses algorithims to control what users see on their news feeds. All users also agree to Facebook’s Terms of Service when they sign up, which does mention that user information can be studied.

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How do you feel after learning you may have been part of a social media experiment? Are you re-considering whether you continue to use Facebook?