A summary of the Facebook study "Experimental evidence of massivescale emotional contagion through social networks" conducted by Facebook and Cornell University is presented below. In this study, Facebook researchers included nearly 700 000 people. The aim of the research was to test the hypothesis that users would experience emotional contagion. The researchers displayed differing amounts of positive and negative posts from the people the users followed, in order to determine whether their subsequent posts were affected by the positivity or negativity of the set of posts they were viewing. The effect was significant; altered newsfeeds demonstrated a slight emotional contagion effect. The Facebook researchers performing the data collection did not seek explicit informed consent from any participants. The experiment was designed by the Cornell researchers and the protocol was carried out by Facebook employees. The Cornell researchers then assisted with data analysis, which the Cornell Institutional Review Board (IRB) considered a "preexisting dataset," and not in need of substantive ethical review. As a private entity not in receipt of federal research funds, Facebook is exempt from review under the Common Rule

What is your opinion about how this study was carried out? Any ethical concerns? Explain.