Facebook caused a stir over the weekend with the revelation that it had been altering the content of some users' News Feeds in an attempt to study the psychology behind what causes people to post emotional material. Now Adam Kramer, Facebook data scientist and co-author of the study, has posted an explanation of the motivation behind the research, which he says serves as Facebook's statement on the matter.

"The reason we did this research is because we care about the emotional impact of Facebook and the people that use our product," says Kramer. "We felt that it was important to investigate the common worry that seeing friends post positive content leads to people feeling negative or left out. At the same time, we were concerned that exposure to friends' negativity might lead people to avoid visiting Facebook."

"In hindsight, the research benefits of the paper may not have justified all of this anxiety."

Kramer notes that the study affected 0.04 percent of users over one week in 2012, though at Facebook's scale that covers hundreds of thousands of people. The study's findings contradicted conventional wisdom, according to the scientist, as seeing positive emotions on Facebook was found to encourage similarly positive content. In a separate statement provided to The Guardian, Facebook said the research was designed to "improve our services and to make the content people see on Facebook as relevant and engaging as possible."

"Having written and designed this experiment myself, I can tell you that our goal was never to upset anyone," says Kramer. "I can understand why some people have concerns about it, and my co-authors and I are very sorry for the way the paper described the research and any anxiety it caused. In hindsight, the research benefits of the paper may not have justified all of this anxiety." Kramer says that Facebook has improved its internal review practices since 2012, and future research will take the reaction to this study into account.