Last week, the Proceedings of the National Academy of Science (PNAS) published a study that conducted a large-scale experiment on Facebook. The authors of the study included an industry researcher from Facebook as well as academics at the University of California, San Francisco and Cornell University. The study employed an experimental design that reduced the amount of positive or negative emotional content in 689,000 Facebook users’ news feeds to test whether emotions are contagious. The study has since spawned a substantial controversy about the methods used, extent of its regulation by academic institutions’ review board, the nature of participants’ informed consent, the ethics of the research design itself, and the need for more explicit opt-in procedures.