Facebook confronted more criticism Thursday as the editor of a scientific journal issued a statement suggesting the company failed to obtain "informed consent" for a controversial study of users' emotions.

As a private company, Facebook wasn't obliged to adopt the strict safeguards that government and academic scientists must use when testing human subjects, said the editor of the Proceedings of the National Academy of Sciences, which published the Facebook study earlier this month.

But journal editor Inder Verma added: "It is nevertheless a matter of concern that the collection of data by Facebook may have involved practices that were not fully consistent with the principles of obtaining informed consent and allowing participants to opt out."

Facebook researchers initially said users had consented by agreeing to the company's data policy when they opened their accounts, although the policy at the time only said Facebook might use members' information to improve or develop new services.

Chief Operating Officer Sheryl Sandberg apologized Wednesday for what she called poor communication about the study, but she said it was no different from other product testing that online companies conduct routinely.

Critics complain Facebook was tinkering with the emotional health of about 700,000 users when it tested their reactions by reducing the positive or negative updates from friends in their news feeds for one week.


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Also on Thursday, a privacy watchdog group filed a formal complaint with the Federal Trade Commission, alleging the study violated a 2012 legal order that settled earlier charges of Facebook privacy abuses. European regulators are reviewing the study, but the FTC has not said whether it will investigate.

Contact Brandon Bailey at 408-920-5022; follow him at Twitter.com/BrandonBailey.