The journal that published a study by Facebook and two U.S. universities about how people's moods spread on the social network is now expressing reservations about the paper.
The Proceedings of the National Academy of Sciences says that as a private company, Facebook had no obligation to adhere to rules on the use of human subjects in the study. But the journal says Facebook's data collection practices may have violated scientific principles requiring the consent of study subjects.
Facebook allowed researchers to manipulate the content that appeared in the "news feed" of about 700,000 randomly selected users during a week in January 2012.
The data-scientists were trying to collect evidence to prove their thesis that people's moods could spread like an "emotional contagion" depending on what they were reading.