Minimizing Disclosure Risk in HHS Open Data Initiatives. III. Providing Access to Government Data


Since the re-identification risk that might result from the mosaic effect more often involves microdata—that is, individual records representing persons or organizations—than tabular data, this chapter focuses on disclosure avoidance procedures for microdata. 11 In this chapter we discuss procedures, methods and techniques that federal agencies and other data holders may use to avoid disclosure of confidential information in microdata. The main reference for federal practice in this area is Statistical Policy Working Paper 22 (FCSM 2005), particularly Chapters III (“Current Federal Statistical Agency Practices”) and V (“Methods for Public-Use Microdata Files”). In Chapter III of the working paper, fourteen federal agencies from across governmental departments reported their data disclosure avoidance practices. This information was collected in 2004, and during the past 10 years the agencies may have modified some of their practices. Mathematica contacted these fourteen agencies to collect information regarding any updates to these practices. Of the 11 agencies that release public use microdata, 6 reported at least some modification of their procedures, although these were generally minor. For the 5 that reported no updates, the descriptions provided in 2004 remain accurate, but in some cases the earlier practices were described in broad terms that could encompass at least some level of revision (for example, citing procedures documented in a separate manual). It is possible, too, that the responses in some cases reflected a reluctance to make public the specifics of the disclosure techniques that are applied to the agency data, as this information could be of use in an attempted re-identification. Table D.1 in Appendix D provides a summary of the earlier practices as well as the reported updates.

We begin by discussing the principal forms of access that federal agencies provide to users of their microdata and then provide an overview of the methods used to protect public use files. We conclude with a brief summary of recent advances in protecting microdata.

11 Strategies for tabular data are discussed briefly in Chapter V and in Appendices C and D.

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