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Patients who suffer a heart attack (acute myocardial infarction, AMI) often benefit from invasive surgical procedures, such as cardiac catheterization, angioplasty, and coronary artery bypass graft (CABG) surgery. Use of these procedures varies, however, among different groups of patients. John M. Brooks, Ph.D., of the University of Iowa, Mark McClellan, Ph.D., M.D., of Stanford University, and Herbert S. Wong, Ph.D., a senior economist at the Agency for Healthcare Research and Quality, teamed up to assess whether these invasive therapies are over- or underused and whether and how use varies by payer group.
The researchers estimated the "marginal" benefits for patients covered by five payer groups: private non-HMO health plans, private HMO plans, Medicare, Medicaid, and self-pay (i.e., no insurance coverage). Data for the study are from hospital inpatient discharge records from the Washington State Inpatient Database, one in a set of 22 State Inpatient Databases (SID) that are part of AHRQ's Healthcare Cost and Utilization Project (HCUP). Over 30,000 patients who were treated for heart attacks in hospitals in the State of Washington between 1989 and 1994 were included in the study.
Marginal benefits are the average benefits for patients on the "extensive margin." Such patients can be thought of as those who would receive treatment next if the treatment rates were increased or those who would be first to lose treatment if the treatment rates were lowered. Estimates of significant treatment benefits for patients on the extensive margin would suggest that the treatment may be underused and should be expanded. Alternatively, negligible estimates of treatment benefits for these patients would suggest that the treatment may be overused and should be discouraged.
The results of this study show that patients in the insurance group with the greatest estimated marginal benefits, controlling for clinical factors, are self-pay patients. Next are Medicare patients, followed by privately insured HMO, Medicaid, and privately insured non-HMO patients. According to the authors, differences in the generosity of reimbursement by different payers may help explain the differences observed among patients with different types of coverage. The rank order by marginal benefits is roughly inversely related to the expected generosity of the insurers' payments to providers. These findings suggest that increasing the rate of invasive surgery for uninsured heart attack patients would yield the largest benefits, and that increasing the rate of invasive surgery for privately insured non-HMO heart attack patients would yield the least benefits.
Of special interest to researchers, this study also demonstrates the value of using an analytic tool called "instrumental variable (IV) estimation" for assessing the marginal benefits of treatments for other conditions. The authors point out the usefulness of IV-based estimates to help policymakers evaluate whether a treatment has been over- or underused within a population. They caution, however, that further research is needed before the results of this study can be used for specific policy recommendations.
See "The marginal benefits of invasive treatments for acute myocardial infarction: Does insurance coverage matter?" by Drs. Brooks, McClellan, and Wong, in the Spring 2000 Inquiry 37, pp. 75-90.
Reprints (AHRQ Publication No. 00-R039) are available from the AHRQ Publications Clearinghouse.
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