infrastructure to support the secure exchange of health information across health IT systems (e.g., electronic health records) and organizations heightens privacy and security concerns because the accessibility of information may increase the potential for access and misuse by authorized and unauthorized users. Concern for patient privacy has led to numerous federal laws and state statutes and regulations on the proper use and disclosure of patient information with which care providers and data collection systems must contend. Although important to patient privacy, the often inconsistent nature of these protections, which leave the decision of whether or not to disclose requested patient information open to various interpretations, may result in discrepancies in data sharing and reporting across states and providers. Such discrepancies may influence the availability and quality of data needed to monitor trends in health care coverage and utilization.

A third challenge to combining data from multiple data systems relates to differences in the way that the systems operationalize data elements or define concepts to allow them to be measured. In addition, linkage between sources at the individual subject level may be uncertain or impossible, and even when linkages with high levels of certainty are possible, all of the relevant information may not be available on all subjects. Furthermore the level of precision of information may not be equal across studies and optimal estimation may have to take this into account as well (IOM, 2012).

Despite significant challenges such as these, advances are being made in the linkage and analysis of data from multiple disparate data systems. A number of large data linkage initiatives are under way, including linkages between the MSIS and the Current Population Survey; MSIS and NHIS; MSIS and the MEPS; survey data from the National Center for Health Statistics (NCHS) and death certificate records from the National Death Index; and survey data from NCHS and claims data from CMS (O’Grady and Mahmud, 2011).

On a smaller scale, the Louisiana Public Health Information Exchange (LaPHIE), described in the committee’s first report (IOM, 2012, Chapter 5), overcame technical and privacy barriers to implement electronic exchange of electronic medial record data and surveillance data between the Louisiana State University Health Care Services Division and the Louisiana Office of Public Health in order to identify people with HIV who have not been linked to or have fallen out of care (Herwehe et al., 2012). On a more general level, the Indiana Network for Patient Care has established the feasibility of linking records across different systems by successfully linking data from hospitals, public health departments, and state Medicaid programs (McDonald et al., 2005).

Ongoing research to develop “new” methodologies to address the statistical challenges of combining data sets, as well as financial and policy support, will be needed to ensure the sustainability of current linkage initia-

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