Validation of Health Event Capture in the Marshfield Epidemiologic Study Area.

OBJECTIVE In this study, health event capture is broadly defined as the degree to which a group of people use a particular provider network as their primary source of health care services. The Marshfield Epidemiologic Study Area (MESA) is a valuable resource for population-based health research, but the completeness of health event capture has not been validated in recent years. Our objective was to determine the current level of outpatient and inpatient health event capture by Marshfield Clinic (MC) facilities and affiliated hospitals for people living within MESA. DESIGN A stratified sample survey with strata defined by MESA region (Central or North) and age group (<18 years or ≥18 years). SETTING 24 ZIP codes in central and northern Wisconsin, USA. PARTICIPANTS 2,485 individuals participated of the 4,313 sampled cohort members residing in MESA Central (N=61,041) and MESA North (N=25,906) on February 22, 2011. METHODS A health care utilization survey was mailed to a random sample stratified by age group and MESA region. Telephone interviews were attempted for nonrespondents. The survey requested information on sources of outpatient care and overnight hospital admissions. Population proportions representing health event capture metrics and corresponding 95% confidence intervals (CI) were estimated with analytic weights applied to account for the survey design. RESULTS Among those with an outpatient visit during the past 24 months, the most recent visit of an estimated 93% (95% CI, 91% - 94%) was at a MC facility. The most recent admission of an estimated 93% (95% CI, 90% - 96%) of those hospitalized in the past 24 months was at a hospital affiliated with MC. The proportion admitted to MC affiliated hospitals was higher for residents of MESA Central (97%) compared to MESA North (83%). CONCLUSION A high proportion of outpatient visits and inpatient admissions in MESA Central and MESA North are accessible in the MC electronic health record. This pattern of high health event capture has been demonstrated since the inception of MESA in 1991. The results from this study validate and support the continued use of MESA for population-based epidemiologic and clinical research.