Medication effectiveness studies in the United States Veterans Administration health care system: A model for large integrated delivery systems

The Veterans Administration health care system (VA) is one of the largest integrated delivery systems in the United States. The VA provides a rich central data base repository that includes detailed medication data, historical information about patient morbidities, clinical data, and inpatient and outpatient utilization information from claims data and health status information derived directly from the patient. The Veterans Health Study (VHS), a large-scale prospective study following patient's health outcomes for up to six years, derived and validated a number of patient questionnaires for wide-scale use in the VA as part of its quality monitoring and research programs. Chief among these assessments are the Veterans Rand 36 item and 12 item health surveys (VR-36 and VR-12); other assessments include measures of illness and their associated severity, health-related quality of life, and utilization of health care services. This report reviews the methodologies developed in the VHS and their subsequent applications in the VA system for conducting medication effectiveness studies based upon non-randomized prospective quasi-experimental designs that approximate real world clinical conditions. Study cohorts are described that link the patient questionnaire data with administrative, clinical, and pharmacy data to address questions about medication effectiveness. Statistical models include comprehensive risk adjustments in order to better understand the association between medications that are being compared and their associated patient outcomes. Applications of this approach are presented for medication studies in those diagnosed with hypertension, osteoarthritis, low back pain, depression, and schizophrenia. Future implications of this work are described for purposes of quality improvement.