An interdisciplinary team of researchers "investigated publicly available Facebook proﬁles of freshmen undergraduate students within one large state university Facebook network" and invited 188 of those freshmen to be interviewed for a health study. At the end of the interview, they told the freshmen that they had been selected using their public Facebook profiles. "Participant responses included endorsement (19.7%), ﬁne (36.4%), neutral (28.8%), uneasy (9.1%), and concerned (6.1%)." The researchers acknowledge that 6 percent minority but conclude that "publicly available Facebook proﬁles of older adolescents are viewed as public spaces by both the adolescents themselves as well as the legal system."
[Moreno, Megan A., Alison Grant, Lauren Kacvinsky, Peter Moreno, and Michael Fleming. “Older Adolescents’ Views Regarding Participation in Facebook Research.” Journal of Adolescent Health 51, no. 5 (November 2012): 439–444. doi:10.1016/j.jadohealth.2012.02.001]