[bcye]

Afaik only in some instances, in some they were not paid and informed consent is in all cases quite questionable

edit: I think this is something I wouldn't call informed consent: "Of particular concern was that users as young as 13 were allowed to participate in the program. Connecticut Senator Richard Blumenthal criticized Facebook Research, stating "wiretapping teens is not research, and it should never be permissible. This is yet another astonishing example of Facebook’s complete disregard for data privacy and eagerness to engage in anti-competitive behavior.""[1]

1: https://en.m.wikipedia.org/wiki/Onavo