More than 20 million Americans have diabetes.1
The direct (medical services) and indirect (disability and premature death) costs of treating diabetes exceed $130 billion per year.2
Amputations, renal failure, visual loss, stroke, heart attack, and premature death reduce the length and quality of life of patients.3
However, a number of landmark studies have indicated that risk factor control can markedly decrease microvascular, and possibly macrovascular, complications of type 1 and type 2 diabetes.4–7
Consequently, the federal government has set objectives for increased provision of care to persons with diabetes, as well as decreased rates of hospitalizations and complications. These rates are monitored on a population basis, with an emphasis on reducing disparities.3,8
A number of private sector organizations and health care quality coalitions have developed, adopted, or endorsed process and intermediate outcomes for persons with diabetes for use by physicians and health care plans.9–13
However, discerning actual progress in combating the diabetes epidemic has been difficult. National weighted population level reports from sources such as National Health and Nutrition Examination Surveys and Behavioral Risk Factor Surveillance System are generally based on comparisons of cross-sectional data, with risk adjustment for age and gender.14
Therefore, inferences made on changes in cross-sectional results in “quality” and “outcomes” can be biased by trends in “case mix.” For example, improvement in rates of diabetes-related adverse outcomes or intermediate outcomes of quality of care could result either from greater provision of appropriate care and/or an increase in the denominator of persons with incident onset diabetes (primarily type 2). Furthermore, at the regional level, such inferences are sensitive to assumptions about the estimated denominator of persons with diabetes.15
Evaluations of improvement within health care plans may also differ when results of randomized interventions with longitudinal follow-up16
are compared to operational reports using plan data.17
Some of these biases may result from the technical specifications used by the industry to define the denominator for performance measurement, i.e., a sampling frame for measurement that includes individuals who maintain enrollment with minimal disruption. Consequently, those who die within the year or leave the plan for any reason are not included.10
Thus, trends in outcomes based on serial cross-sectional data may be influenced by both in- and outmigrations of enrollees, in addition to the quality of care provided to enrollees, and inferences regarding performance confounded by selection biases. The Institute of Medicine emphasized that measures and rewards of performance should target multiple dimensions of care, initially including measures of technical quality, patient-centered care, and efficiency but transitioning toward longitudinal and health-outcome measures.18
Current national and industry snapshots are inadequate to meet this challenge; another approach is needed.
The Veterans Health Administration (VHA) provides a national laboratory in which to study trends in intermediate risk factor management and disease outcomes of diabetes on a national population level.19
The VHA provides comprehensive health care services to almost five million veterans annually and has the most advanced electronic health record in the United States.20
Although most veterans who are users of the VHA system maintain some continuity of care within the VHA, more than half these patients are also enrolled in the federal Medicare program because of either age (65 years or older) or disability.21
For veterans with diabetes, this percentage rises to nearly three in four patients. Thus, in order for researchers to be able to obtain a more complete picture of these patients′ health care and outcomes, it is necessary to include Medicare claims with VHA patient data for care in the same period. While Medicare administrative data are not as rich as the clinical information in databases of the VHA, their utilization addresses continuity of follow-up and thus provides more accurate estimates of complication rates and resource utilization.
The Diabetes Epidemiologic Cohort (DEpiC) is a research database of all VHA patients with diabetes from 1997 to 2006.22
The objectives of the DEpiC are to determine diabetes prevalence and incidence, provide surveillance of rates of diabetes-related morbidity and mortality, and evaluate time-varying predictors of diabetes-related morbidity and mortality in the veteran population. The DEpiC has also been used to evaluate variation in the quality of diabetes care and outcomes with variation in race/ethnicity, mental health status, and other comorbidities and to advance methodological issues related to the use of computerized patient data for epidemiology and health services research.23–42
In addition, the DEpiC is unique because of its size (over 1.5 million veterans with diabetes), national scope, and overrepresentation of individuals who are poor or have mental health conditions. This article reports on methodology used to develop the DEpiC and describes findings of methodological and policy importance in the evaluation of glycemic control and lower extremity amputations.