In a series of methodological papers, we have described the Rochester Epidemiology Project (REP) medical records-linkage system as it has existed for more than 50 years in Olmsted County, Minnesota.1–4 Further details about the major events and protagonists of the history of the original REP are available elsewhere.1 Starting in 2010, we have expanded the population captured by the REP from a single county in south-eastern Minnesota to a geographical region including 27 counties in southern Minnesota and western Wisconsin. In this paper, we provide a profile of the expanded medical records-linkage system, which we name the Expanded-REP (E-REP) to distinguish it from the original REP. Because the data became available for electronic linkage and storage starting in 2010, we can consider 2010 the birth year for the E-REP. The E-REP was established to provide longitudinal medical data for a population residing in a well-defined geographical region. The E-REP captures a large percentage of the persons who have resided in a 27-county region of southern Minnesota and western Wisconsin at some time from 1 January 2010 to the present, regardless of age, sex, ethnicity and disease status. Depending on the needs for a specific study, the region can also be partitioned into smaller segments. For example, some studies have targeted a seven-county region or an 11-county region because these regions have a higher percentage of population capture; therefore, the non-participation percentage is lower.5–7 The electronic indexes of the E-REP include not only demographic information, diagnostic and procedure codes, health services utilization data and outpatient drug prescriptions, but also results of laboratory tests and information about smoking, height, weight and body mass index. Table 1 shows a list of data that are currently included in the electronic indexes and their definitions. List of characteristics captured electronically within the electronic indexes of the E-REP ICD, International Classification of Diseases; CPT, Current Procedural Terminology; HCPCS, Healthcare Common Procedure Coding System. The full address is also available as longitude and latitude (geocoding) for linkage with data from the US Census and the American Community Survey. Other and mixed race includes those persons who specified ‘Two or more races’ in the US Census and persons who specifically reported their race as ‘Other’ or ‘Mixed’ in the E-REP. No category for ‘Unknown’ race exists in the US Census. The persons in the E-REP population with Unknown race include 940 persons who refused to specify a race, and 28 311 persons for whom no race information was available from any of their medical records. All persons who did not declare to be Hispanic, were considered non-Hispanic. Education is available for 46.1% of the E-REP population aged 25 years or older. Patient-provided smoking status is collected in different ways across institutions. Therefore, smoking status is normalized to meaningful use categories before incorporation into the REP indexes. All medical data include the date on which each piece of information was collected. We use the National Library of Medicine RxNorm standard nomenclature [http://www.nlm.nih.gov/research/umls/rxnorm]. Drug prescriptions are also assigned to a National Drug File Reference Terminology (NDF-RT) category. Once standardized, prescriptions can be retrieved by RxNorm code, NDF-RT category or specific ingredient using REP tools. The standard nomenclature LOINC system is complex and not intuitive. Therefore, we have developed a customized retrieval software for 55 common laboratory tests based on test name. We have validated our methods against the CPT codes for the same test to ensure that investigators receive the results for all of the laboratory tests that were actually performed. List of characteristics captured electronically within the electronic indexes of the E-REP ICD, International Classification of Diseases; CPT, Current Procedural Terminology; HCPCS, Healthcare Common Procedure Coding System. The full address is also available as longitude and latitude (geocoding) for linkage with data from the US Census and the American Community Survey. Other and mixed race includes those persons who specified ‘Two or more races’ in the US Census and persons who specifically reported their race as ‘Other’ or ‘Mixed’ in the E-REP. No category for ‘Unknown’ race exists in the US Census. The persons in the E-REP population with Unknown race include 940 persons who refused to specify a race, and 28 311 persons for whom no race information was available from any of their medical records. All persons who did not declare to be Hispanic, were considered non-Hispanic. Education is available for 46.1% of the E-REP population aged 25 years or older. Patient-provided smoking status is collected in different ways across institutions. Therefore, smoking status is normalized to meaningful use categories before incorporation into the REP indexes. All medical data include the date on which each piece of information was collected. We use the National Library of Medicine RxNorm standard nomenclature [http://www.nlm.nih.gov/research/umls/rxnorm]. Drug prescriptions are also assigned to a National Drug File Reference Terminology (NDF-RT) category. Once standardized, prescriptions can be retrieved by RxNorm code, NDF-RT category or specific ingredient using REP tools. The standard nomenclature LOINC system is complex and not intuitive. Therefore, we have developed a customized retrieval software for 55 common laboratory tests based on test name. We have validated our methods against the CPT codes for the same test to ensure that investigators receive the results for all of the laboratory tests that were actually performed. The E-REP includes medical record data from multiple health care institutions, and these institutions currently use four distinct electronic health record (EHR) systems: the Mayo Clinic GE Centricity EHR, the Olmsted Medical Center IC Chart EHR, the Mayo Clinic Health System Cerner EHR and the Olmsted County Public Health Services PH-Doc EHR. The Mayo Clinic and the Mayo Clinic Health System are currently transitioning to a shared EPIC EHR system that will simplify the linkage greatly. In addition, the Olmsted Medical Center is also transitioning to an EPIC EHR (similar but less customized than the Mayo Clinic version), which will make the data more homogeneous. We have more than 50 years of experience in linking data derived from different health care institutions and different EHRs, and the general methods used have been described in detail elsewhere.4 The studies conducted to validate the linkage methods in the original REP showed a frequency of failure to link two records when the records belonged to the same person (under-inclusion rate) of 1.3% [95% confidence interval (CI): 0.2-2.4%], and a frequency of incorrect linkage of two records when the records did not belong to the same person (over-inclusion rate) of 2.5% (95% CI: 1.0-4.0%).4 We also validated the census enumeration based on address information.4 A team with information technology and statistical expertise is dedicated to the E-REP (approximately three full-time equivalent positions). All unique persons who had at least one health-related visit captured by the system after 1 January 2010 were considered to enumerate the 27-county population using the individual timeline methods described elsewhere.4Table 2 shows the population captured by the E-REP on 1 January 2014 and the percentage capture compared with the US Census estimates for 2014, overall and in strata by county and sex. The counties are grouped under Minnesota (19 counties) and Wisconsin (eight counties). In 2014, the E-REP captured 694 506 persons, 337 241 men (48.6%) and 357 265 women (51.4%; Table 2). The largest captured population resides in Olmsted County (n = 150 013) followed by Eau Claire County (n = 56 104) and La Crosse County (n = 51 804). Table 2 also shows the population captured and the percentage capture for a seven-county region with higher coverage. Population captured within the Expanded Rochester Epidemiology Project (E-REP) and percentage capture as compared with the 2014 US Census estimates (1 January 2014)a This table includes only persons who have given permission for all or part of their medical record information to be used for research purposes (participants in the E-REP). The complete population enumerated by the E-REP on 1 January 2014 comprised 763 695 persons (369 403 men and 394 292 women); therefore, the participation was 90.9% overall, 91.3% for men, and 90.6% for women. Percentage captured is calculated by dividing the E-REP population by the US Population Census Estimates (Vintage 2015) for 1 July 2014, as reported in Supplementary Table 3 (available at IJE online). These are the counties included in the seven-county region. Population captured within the Expanded Rochester Epidemiology Project (E-REP) and percentage capture as compared with the 2014 US Census estimates (1 January 2014)a This table includes only persons who have given permission for all or part of their medical record information to be used for research purposes (participants in the E-REP). The complete population enumerated by the E-REP on 1 January 2014 comprised 763 695 persons (369 403 men and 394 292 women); therefore, the participation was 90.9% overall, 91.3% for men, and 90.6% for women. Percentage captured is calculated by dividing the E-REP population by the US Population Census Estimates (Vintage 2015) for 1 July 2014, as reported in Supplementary Table 3 (available at IJE online). These are the counties included in the seven-county region. Supplementary Tables 1 and 2 (available as Supplementary data at IJE online) show the additional stratification by age (strata by county, sex and age). Supplementary Table 3 (available as Supplementary data at IJE online) shows the US Census population estimates used to calculate the percentage capture. The capture was 60.9% overall, was higher in women (62.4%) than in men (59.4%; Table 2) and increased monotonically with older age for both men and women (Supplementary Table 2). There are two primary factors influencing the percentage capture. First, not all of the care facilities providing care to the population residing in the 27-county region collaborate with the E-REP. Second, persons who receive care from any of the participating care facilities located in Minnesota are asked to sign a research authorization form as required by Minnesota law (Minnesota State privacy law, statute 144.335).2,4 The E-REP only includes persons who have given permission for all or part of their medical record information to be used for research purposes (participants in the E-REP); overall, 90.9% of the eligible population provided this authorization (participation of 91.3% for men and 90.6% for women; see footnote a in Table 2). A similar law is not active in Wisconsin. Figure 1 is a map of the 27-county region showing the geographical location and the percentage capture for each county. The region can be subdivided into a maximum capture segment, Olmsted County (99.9%; blue border), a high capture segment, including Olmsted County and six additional contiguous counties (93.8%; seven-county region, pink border) and the complete 27-county region (60.9%). The percentage capture may vary in the coming years with new health care institutions joining the E-REP and with changes in the population. Therefore, the high capture segment may vary across studies conducted at different times. Geographical map of the 27-county region of the E-REP showing the geographical location and the percentage capture for each county (black numbers or white numbers). The region can be subdivided into a maximum capture segment, Olmsted County (blue border), a high capture segment, including Olmsted County and six additional contiguous counties (pink border), and the overall 27-county region. The colour shading of the counties is proportional to the percentage capture of the E-REP as compared with the US Census estimates. Figure 2 shows the distribution in the 27 counties by percentage of persons below poverty level (panel A), percentage of persons of non-White race (panel B), percentage of college-educated persons (panel C) and percentage of county area considered urban. These data were gathered from the US Census Bureau and the American Community Survey.8–11 The expansion from the traditional REP in Olmsted County (highlighted in blue) to the 27-county region will allow the inclusion of greater numbers of people living in poverty, with lower education, of non-White race, and living in more rural areas. Maps with distribution of counties by poverty level, race, education and rurality. Geographical map of the 27-county region showing the distribution by percentage of persons below the poverty level (panel A), percentage of persons of non-White race (panel B), percentage of persons with college degrees (panel C) and percentage of county area considered urban (panel D). These data were gathered from the US Census Bureau and the American Community Survey.8–11 The colour shading of the counties is proportional to the percentage values. The scale varies across the four panels to maximize the visual contrast. Olmsted County is highlighted in blue to facilitate the comparison of the traditional REP with the E-REP. Table 3 shows the percentage capture of the E-REP stratified by race and ethnicity, as specified by the US Census. Overall, the capture rate was higher for Blacks and lower for Asians compared with Whites. However, the E-REP classification of people by race and ethnicity was different from the US Census and for more people to as or In addition, of the population in the E-REP refused to specify a race, or no information was in any of their medical records. Overall, the population had a capture percentage higher than the population. and of the population captured in the Expanded Rochester Epidemiology Project (E-REP) on 1 January 2014 American or or The estimates for 2014 are from the US The capture percentage is calculated by dividing the of persons in the E-REP by the in the US Census. of the capture higher than are to in classification the US Census and the E-REP. In the E-REP more people who as or Other and mixed or had Other and mixed race includes those persons who specified ‘Two or more races’ in the US Census and persons who specifically reported their race as ‘Other’ or ‘Mixed’ in the E-REP. No category for ‘Unknown’ race exists in the US Census. The persons in the E-REP population with Unknown race include 940 persons who refused to specify a race, and 28 311 persons for whom no race information was available from any of their medical records. and of the population captured in the Expanded Rochester Epidemiology Project (E-REP) on 1 January 2014 American or or The estimates for 2014 are from the US The capture percentage is calculated by dividing the of persons in the E-REP by the in the US Census. of the capture higher than are to in classification the US Census and the E-REP. In the E-REP more people who as or Other and mixed or had Other and mixed race includes those persons who specified ‘Two or more races’ in the US Census and persons who specifically reported their race as ‘Other’ or ‘Mixed’ in the E-REP. No category for ‘Unknown’ race exists in the US Census. The persons in the E-REP population with Unknown race include 940 persons who refused to specify a race, and 28 311 persons for whom no race information was available from any of their medical records. Supplementary Table (available as Supplementary data at IJE online) the and characteristics of the 27-county population captured by the E-REP with data from the US Census for the 27-county the population and for the US population in The are also in Figure The part of Figure 3 shows a map of the with the of the highlighted in and The geographical location of the 27-county region is as an on the of Minnesota and Wisconsin. The 27-county region is also of the map in The colour to the 27-county region as reported by the US and the blue colour to the 27-county region as currently captured by the E-REP. of the E-REP population with US Census data for the 27-county region, the and the The part of the shows a geographical map and the colour for the three regions that were compared in this the 27-county region, the and the The 27-county region captured by E-REP included 60.9% of the 27-county population and of the population as by the US Census for In the population of the US population. The of the the 27-county region captured in E-REP with the population for the population of the 27-county region for the and for the The were using age The in the and the for race, ethnicity, and This E-REP data with data from the US Census Bureau and the American Community and are included in the US but are not in the The of Figure 3 shows the population profile for the 27-county region captured by the on the from the US Census for the 27-county region for the population and for the US population The and of Figure 3 show of the 27-county population captured by the E-REP (blue with the three comparison for and the by race, ethnicity, and education were similar for the E-REP population (blue compared with the US Census 27-county population and with the US Census population However, the US population included higher of and compared with the E-REP population. The population of the 27-county region captured by the E-REP has a and distribution similar to the 27-county region as reported by the US that the 60.9% capture not a major for these In addition, the population of the 27-county region captured in the E-REP is similar to the population of the (Supplementary Table available as Supplementary data at IJE and Figure These in distribution that some of from the E-REP population to the and to a large segment of the US population may be However, be on a and the E-REP to link and data only in 2010, a studies have used the new data These studies the for use in In a study, used the E-REP to the of persons years in the 27-county region (n = The results were to the results of a primary care in of the same 27-county region. The showed that and were with the of and at the These data can to in In a study, used the E-REP to in a seven-county region in southern Minnesota 2010 and from address was used to link with data from the American Community at the census age and sex were with higher in with status was with lower of of and of also across the region and were higher in urban areas. The of geographical with may to used an 11-county region in south-eastern Minnesota to the and status or health in with The E-REP electronic indexes were used to all of the persons in the system who an for failure 1 January and These persons were to in a to status and The showed that greater in with failure was with status and of used the same 11-county region in south-eastern Minnesota to the health and in with The E-REP electronic indexes were used to all persons in the system who an for failure 1 January and These persons were to in a to health Health was as or and persons were followed using the E-REP electronic indexes to and The showed that health was with increased of and by These four studies four characteristics of the the of the E-REP to include a of counties as by the specific and by the the to link medical record data with data collected from care or from the to link the address with longitude and latitude and to use the to data from the US from the American Community or from and the to people with a laboratory test or a drug to be to in a in an study, or in a The of research methods electronic medical record data or electronic data and active research methods people for studies or may be for the The major of the E-REP is the and the geographical compared with the original REP. We to the REP from the original region to 27 to the population from 150 people to This to less common specific of the population years or women years and specific and for the comparison of persons residing in rural urban with high percentage of area considered the percentage of in the E-REP region is smaller than in some of the southern or the E-REP includes a of and these can be for specific studies the for some of the and for some less common the numbers may after This may time with the expansion of the of capture of or Therefore, the E-REP to some an of the original REP that not include large numbers of The E-REP also a of the original REP population who include an high percentage of health and their who may have to medical care and a higher level of health We have that the of studies conducted in Olmsted County are in in the and For example, the of a in the of in Olmsted County has been in the and in However, the inclusion of additional counties in rural Minnesota and rural Wisconsin more address the For example, the percentage of persons aged years and the level are similar in the 27-county region captured by the E-REP and in the US population of the E-REP is the more than 50 years of experience linking data from different institutions and different the are and to linkage that will and of the E-REP is the 60.9% population capture. The capture is higher for women than men, for older persons and in some including Olmsted County and six contiguous The capture may a when or the history of or In addition, factors as education, or county of may the capture rate and may the results of studies studies or The is that the population captured may be different from the population not the a similar is in studies that active and participation of in a or in a multiple and The percentage participation in studies at is less than the E-REP and is in or studies may from In addition, some have that is not or not in studies the two using the 27-county region for studies in which a may be an can use an comparison The 27-county region can be partitioned into three Olmsted County, the capture is a seven-county region, the capture is and the overall region, the capture is For example, the rate of a given disease is similar in the three for age and sex it is that the overall results in the 27-county region are The of using the region for a is the increased of persons and the of the a or a can be stratified across the three the or the is the same in Olmsted County, the seven-county region and the 27-county region, we can that are no major However, the or the are we have of a and the or the be reported A similar was used to the geographical area of and the of may the capture in studies using series of to the Mayo Clinic from the region or from Because the E-REP to link and data only in 2010, the maximum of longitudinal data is currently Therefore, studies of one with be conducted studies with that are may a time to an of However, the E-REP will with The E-REP a single US and the of our studies may from those of studies conducted in However, the demographic and characteristics of our population are similar to those of the and of a large segment of the US and of the studies in in the and will allow for In addition, the on a population for the of and The E-REP can be to for and data from the original REP have been used to a Community Health which health The E-REP to these by from the Center for and our population can as a for studies in the This and and the and We developed an that we the REP to of and of The was described in detail and can be the REP at data can be However, large and complex records-linkage the use of the data in the E-REP is We investigators in using the E-REP to test specific to a with our research be to with a of the E-REP in a The E-REP medical records-linkage system is a new data to In 2014, the E-REP captured of the persons residing in a 27-county region of southern Minnesota and western Wisconsin. In 2014, the E-REP included a of 694 506 persons, 337 241 men (48.6%) and 357 265 women of the population is and of a non-White The E-REP electronic indexes include demographic information, diagnostic and procedure codes, health services utilization outpatient drug prescriptions, results of laboratory tests and information about smoking, height, weight and body mass index. The and characteristics of the E-REP population are similar to the characteristics of the 27-county region, of the and of a large segment of the US population. However, of to in the or be considered on a data are available to the REP in using the E-REP to test specific can Supplementary data are available at IJE The Rochester Epidemiology Project is by the National on of the National of Health numbers However, the of this is the of the and not the of the National of This was also by from the Mayo Clinic and Center for the of Health was by the National of Health and We for in and the and are the of the REP and all of the and are for data linkage and also statistical to of the E-REP. expertise in health and the and all of the provided of the of