We sought to determine whether all diagnoses and total illness burden of patients who use both the VA and Medicare health care systems can be obtained from examination of data from only one of these systems.
Cohorts included all age-eligible Medicare users who also used the VA health care system in fiscal years 2000–2002 but were not enrolled in a Medicare HMO. Relative risk scores (RRS; a measure of illness burden developed by DxCG, Inc., Boston, MA) were calculated using VA, Medicare, and all diagnoses from both VA and Medicare data sources. The relationship between RRS and reliance on Medicare versus the VA system also was explored. We explored whether differences in VA and Medicare RRS were caused by veterans who mainly used pharmacy services or by an underweighting in the RRS calculation of mental health diagnoses. Finally, we explored the relationship between inpatient utilization and RRS in each system.
On average for a given patient who used both VA and Medicare services, more diagnoses were recorded in Medicare (∼13–15) than in the VA system (∼8) for dual users. On average only 2 diagnoses were common to both the VA and Medicare. Medicare data alone accounted for approximately 80% of individuals’ total illness burden, and VA data alone lead to RRSs that capture one-third of the total illness burden. The ratio of RRS when calculated using Medicare and VA separately was approximately 2.4. RRS was only weakly to moderately correlated with inpatient utilization in each system.
Using data from just Medicare or VA data sources when conducting research on dually eligible veterans may seriously underestimate total illness burden of the population and also may lead to an underidentification of individuals in a particular disease class.
From the *Department of Epidemiology and Public Health, University of Miami, Miami, Florida; and †Division of Health Policy and Quality, Houston Center for Quality of Care and Utilization Studies, a Health Services Research and Development Center of Excellence, Houston VA Medical Center, and Section for Health Services Research, Baylor College of Medicine, Houston, Texas.
Supported by the Department of Veterans Affairs (Project XVA 33-093). The funding agreement ensured the authors’ independence in designing the study, interpreting the data, writing, and publishing the report. The views expressed are solely those of the authors and do not necessarily represent those of the VA. Dr. Petersen is a Robert Wood Johnson Foundation Generalist Physician Faculty Scholar (grant number 045444) and a recipient of the American Heart Association Established Investigator Award. Dr. Byrne holds a National Cancer Institute career development award (CA101812-02).
Reprints: Margaret M. Byrne PhD, Department of Epidemiology and Public Health, PO Box 016069 (R-669), University of Miami, Miami, Florida 33101. E-mail: email@example.com.