The scientific journal that published a controversial Facebook experiment on mood manipulation said Thursday it was concerned that the company did not follow scientific ethics and principles of informed consent. While it stopped short of retracting the study, the Proceedings of the National Academy of Sciences said it typically publishes experiments that have allowed subjects to opt out of research. Facebook appeared to have been exempt from this rule because all users agree to a policy on data use when they open an account, constituting informed consent for research, according to PNAS. Based on the information provided by the authors, PNAS editors deemed it appropriate to publish the paper, said a statement by editor-in-chief Inder Verma.