Reidentification of Individuals in Chicago’s Homicide Database: A Technical and Legal Study

Abstract

Many government agencies, hospitals, and other organizations collect personal data of a sensitive nature. Often, these groups would like to release their data for statistical analysis by the scientific community, but do not want to cause the subjects of the data embarrassment or harassment. To resolve this conflict between privacy and progress, data is often deidentified before publication. In short, personally identifying information such as names, home addresses, and social security numbers are stripped from the data. We analyzed one such deidentified data set containing information about Chicago homicide victims over a span of three decades. By comparing the records in the Chicago data set with records in the Social Security Death Index, we were able to associate names with, or reidentify, 35% of the victims. This study details the reidentification method and results, and includes a legal review of U.S. regulations related to reidentification. Based on the findings of our project, we recommend removal of these databases from their online locations, and the establishment of national deidentification regulations.