A Social Networks Theory of Privacy

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What facts are public and what facts are private? It is the fundamental, first-principles question in privacy law, and a necessary element in the two most important privacy torts, public disclosure of private facts and intrusion upon seclusion. Yet the American courts lack a coherent, consistent methodology for determining whether an individual has a reasonable expectation of privacy in a particular fact that he has shared with one or more persons. Some courts hold that when an individual discloses a sensitive fact about himself to a handful of co-workers, friends, relatives, or strangers, this disclosure renders the fact in question sufficiently public to deprive him of a tort cause of action when that fact is subsequently widely disseminated or obtained by a third party using improper means. Other courts hold that an individual can share such a fact with dozens, or even hundreds of people, and still retain a cause of action under privacy tort law. So how much disclosure is enough to transform a private fact into a public fact? This paper argues that insights from the literature on social networks and information dissemination can help provide courts with satisfying answers to these central questions in privacy law. The social networks literature has generated theoretical and empirical insights about the probability that information disclosed to one member of a community will ultimately become known by a large segment of the community. Using these insights, courts can gauge whether the plaintiff's previously private information would have been widely disseminated regardless of the defendant's actions in a particular case. If so, the information in question was public, and if not, the tort law ought to deem the information as private. This paper argues that such an approach, which treats the privacy question as an empirical one, is more attractive than any other method of establishing whether the plaintiff had a reasonable expectation of privacy in the information at issue. The literature on social networks and information dissemination has wide applications beyond privacy tort law, but has found its way into little legal scholarship. Legal scholars interested in Fourth Amendment law, trade secrets, patent law, constitutional privacy, defamation, and other fields might find the paper's survey of social networks theory useful and provocative.