In connection with a psychological experiment facebook manipulated in January 2012 the message stream of hundreds of thousand users. This causes outrage of many users which facebook tries to compensate by “proofing” that the experiment as done with a strict internal supervision.
During the one week lasting experiment in January 2012 facebook wanted to perform a research how emotions are distributed in the social network. According to this facebook pre-filtered message streams by presenting one group more positive messages and the other group more negative messages. The result of the study was that users who received more positive messages tended also to publish positive messages by themselves and vice versa. One of the authors of the study stated, that facebook wanted to know if users tend to leave the social network in case they receive more negative messages.
All in all 690.000 users from the English speaking faceboook version where involved in this experiment and hence where manipulated without their approval. The software analyzed more than 3 million posts in order to receive the above mentioned result.