Use of a medical records linkage system to enumerate a dynamic population over time: the Rochester epidemiology project

Abstract

The Rochester Epidemiology Project (REP) is a unique research infrastructure in which the medical records of virtually all persons residing in Olmsted County, Minnesota, for over 40 years have been linked and archived. In the present article, the authors describe how the REP links medical records from multiple health care institutions to specific individuals and how residency is confirmed over time. Additionally, the authors provide evidence for the validity of the REP Census enumeration. Between 1966 and 2008, 1,145,856 medical records were linked to 486,564 individuals in the REP. The REP Census was found to be valid when compared with a list of residents obtained from random digit dialing, a list of residents of nursing homes and senior citizen complexes, a commercial list of residents, and a manual review of records. In addition, the REP Census counts were comparable to those of 4 decennial US censuses (e.g., it included 104.1% of 1970 and 102.7% of 2000 census counts). The duration for which each person was captured in the system varied greatly by age and calendar year; however, the duration was typically substantial. Comprehensive medical records linkage systems like the REP can be used to maintain a continuously updated census and to provide an optimal sampling framework for epidemiologic studies.

Figure 1.

Steps involved in linking medical records from multiple care providers to unique residents of Olmsted County, Minnesota, 1966–2008. The lower part of the figure shows an example of a timeline for a person who entered the system in 1966 at the age of 42 years, lived in and out of Olmsted County for a number of years, and died in 1984 at age 60 years while residing in the County (green arrow).

Figure 2.

Procedures used to link multiple medical records to single individuals in the Rochester Epidemiology Project from 1966 to 2008. The 20 rounds of exact matching are presented in hierarchal order from the most perfect match to the least perfect match.

Figure 3.

Age- and sex-specific capture rate by the Rochester Epidemiology Project (REP) medical records linkage system compared with US Census data (median capture rate in 1970, 1980, 1990, and 2000). Data from men (solid line, circle points) and women (dashed line, square points) are shown separately. The 0% line corresponds to perfect agreement between the system and the US Census. Values plotted above the 0% line indicate that the REP counted more persons than the US Census; values plotted below the 0% line signify that the REP counted fewer persons than the US Census.

Figure 4.

Age- and sex-specific mortality rates for Olmsted County in 2000 computed using Rochester Epidemiology Project data (solid line) compared with rates derived from national vital statistics data (dotted line). Mortality rates are shown separately for men (left panel) and women (right panel).