Sharing Medical Data

Weaving Technology and Policy Together to Maintain Confidentiality

by Latanya Sweeney, Ph.D.


Often organizations release and receive medical data with all explicit identifiers, such as name, address, phone number, and Social Security number, removed in the incorrect belief that patient confidentiality is maintained because the resulting data look anonymous; however, we show that in most of these cases, the remaining data can be used to re-identify individuals by linking or matching the data to other databases or by looking at unique characteristics found in the fields and records of the database itself. When these less apparent aspects are taken into account, each released record can be made to ambiguously map to many possible people, providing a level of anonymity which the user determines; the greater the number of candidates per record, the more anonymous the data. We examine three general-purpose computer programs for maintaining patient confidentiality when disclosing electronic medical records: the Scrub System which locates personally-identifying information in letters between doctors and notes written by clinicians; the Datafly System which generalizes values based on a profile of the recipient at the time of access; and, the Mu-Argus System which is becoming a European standard for disclosing public use data. Despite the possible effectiveness of these systems, completely anonymous data may not contain sufficient details for all uses, so care must be taken when released data can identify individuals and such care must be enforced by coherent policies and procedures.

Keywords: computer science research, privacy, technology, human subjects, IRB, privacy technology, data privacy

L. Sweeney. Weaving Technology and Policy Together to Maintain Confidentiality. Journal of Law, Medicine & Ethics, 25, nos. 2&3 (1997): 98-110. (

An earlier version of the paper above appears as:
L. Sweeney. Maintaining Patient Confidentiality When Sharing Medical Data Requires a Symbiotic Relationship Between Technology and Policy. Artificial Intelligence Laboratory, Massachusetts Institute of Technology, AIWP-WP344, May 1997. (PDF)

Related Links

Tell me more about:

Spring 2004 []