That pang in your heart? That is the feeling of being unfriended by your former best friend on Facebook.

The University of Colorado Denver surveyed over 1,000 people on Twitter to shed new light on the friends we unfriend on Facebook and their emotional responses to it.

Participants were recruited on Twitter by sending users a reply to a tweet that used the terms “unfriend,” “defriend” or “unfriending.” Since much of Twitter is public, this made it easier to find potential participants, particularly those who were recently unfriended and could accurately recall their emotions.

High school friends were the first to go. Christopher Sibona, a doctoral student at the CU Denver Business School believes one of the reason high school friends are unfriended are due to strong religious and political beliefs. “One thing about social media is that online disagreements escalate much more quickly,” said Sibona.

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This is a good lesson for brands too. Don’t be polarizing in your posts -- it’s very likely to lead to an “unlike.” Unless you are in the business of religion and politics, just stay away.

Co-workers are unfriended not because of what they do on Facebook, but for their actions in the real world, the survey found. For example, if a co-worker treats you poorly at work, you may be more likely to unfriend them once one of you gets a new job.

The second part of the study looked at the emotional response to being unfriended. The most common response was, “I was surprised.” How you feel about an unfriending depends on how close you were to the person at the time of the unfriending. Obviously, you’re bound to feel more strongly about being unfriended by your best friend than someone you met at a party four years ago.  

Other common responses were: “It bothered me,” “I was amused,” and “I felt sad.”

According to the research, more unfriending happens between friends who were once closer rather than acquaintances.

Sibona said the real world consequences of unfriending warrant additional research.

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