Minimizing Disclosure Risk in HHS Open Data Initiatives. Executive Summary


Federal agencies have a long history of releasing data to the public, and they also have a legal obligation to protect the confidentiality of the individuals and organizations from which the data were collected. Federal agencies have successfully balanced these two objectives for decades. With the new emphasis on expanding public access to federal data, coupled with the increasing availability of data from other sources, federal agencies are continuing to ensure that the combination of data already available and the data they are preparing to release does not enable the identification of individuals or other entities through what has been termed the “mosaic effect.” The concept of a mosaic effect is derived from the mosaic theory of intelligence gathering, in which disparate pieces of information become significant when combined with other types of information (Pozen 2005).

To gain more insight into the mosaic effect and its implications for the continued release of data to the public while minimizing the risk of disclosing personal information, the Office of the Assistant Secretary for Planning and Evaluation (ASPE) in the U.S. Department of Health and Human Services (HHS) contracted with Mathematica Policy Research to convene a technical expert panel (TEP), prepare background materials, and summarize what was learned from the panel discussion and the background research in a final report. The goals of the project were (1) a balanced and scientifically sound assessment of the mosaic effect, (2) identification of any unique increased risk associated with the mosaic effect, and (3) identification of data release policies and best practices that can prevent or reduce disclosure due to the mosaic effect.

In assessing the increased risk that open data initiatives may create or incur through the mosaic effect, we and our expert panelists reviewed what is known about the sources of disclosure risk and the effectiveness of various ways to control such risk. From the discussion at the TEP meeting and the materials we reviewed in preparing the two background papers, we prepared a synthesis, which is followed by concluding observations.


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