79 Health Economics A Time-tradeoff Method for Cost–Effectiveness Models Applied to Radiology J. SHANNON SWAN, MD, DENNIS G. FRYBACK, PhD, WILLIAM F. LAWRENCE, MD, FRANC ¸ OIS SAINFORT, PhD, MARY ELLEN HAGENAUER, DENNIS M. HEISEY, PhD Purpose. The wait tradeoff (WTO) is a simple time-tradeoff method designed for tem- porary health states that uses a realistic and intuitive interface for the patient/subject. This method was tested by assessing patients’ preferences for magnetic resonance angiography (MRA) versus x-ray angiography (XRA). Materials and methods. The WTO was tested by telephone interview in 38 patients with atherosclerotic peripheral vascular disease, all having previously undergone both MRA and XRA. At indifference point, patients were ambivalent about having MRA or XRA and immediate treatment, versus having a waiting period for test results and treatment after a hypothetical ‘‘ideal test’’ that entailed no pain or risk. Results. The patients were willing to wait a mean of 42.1 days after the ideal test for results and treatment, as opposed to XRA. They were willing to wait only 16.1 days as opposed to MRA. This difference in waiting times was significant ( p = 0.0001) and indicates a clear preference for MRA, in agreement with known literature. Conclusion. The WTO method assesses preferences for these ra- diologic tests in an intuitive fashion that does not invoke artificial or irrelevant health states. This approach may also prove useful for other testing situations or short-term treatments being evaluated for cost–effectiveness. Key words: cost–effectiveness; util- ity assessment; magnetic resonance; angiography; technology assessment; time tradeoff. (Med Decis Making 2000;20:79–88) Cost–effectiveness analysis (CEA) has become an im- portant measure of the value of health care pro- grams. 1 When quality of life is considered, CEA re- sults are generally expressed in terms of dollars per quality-adjusted life year ($/QALY). The aim is to gain the most QALYs with the least cost. Costs can be ascertained with various methods, which differ de- pending on the perspective of the analysis. Defining the QALYs that are appropriate for the programs be- ing compared may also be done with various meth- ods, but this can be particularly challenging. While Received December 16, 1998, from the Department of Radi- ology, Indiana University, Indianapolis (JSS); the Departments of Preventive Medicine (DGF, FS), Industrial Engineering (DGF, FS), Radiology (MEH), and Surgery (DMH), University of Wisconsin– Madison; and the Lombardi Cancer Center and Control, De- partment of Medicine, Georgetown University, Washington, DC (WFL). Revision accepted for publication July 19, 1999. Supported by the National Heart, Lung, and Blood Institute (R01 HL51370 — JS Swan, PI). Address correspondence and reprint requests to Dr. Swan: Indiana University Medical Center, Department of Radiology, 550 North University Boulevard, Indianapolis, IN 46202; telephone: (317) 278-4920; e-m ail: jsswan@ iupui.edu. QALYs have a basis in mathematical formalism, they are subjective in their origin with patients’ or a com- munity’s utilities 2 for states of health. To generate QALYs, one must define these preferences over a period of time, whether the health state of interest in the analysis is the morbidity of a test, the outcome of surgery, or chronic disease. Traditional utility measurement has focused to a large degree on the measurement of chronic health states. Traditional methods of assessing preferences for health states assume that the health state stays constant over time. More difficult conceptually is the measurement of short-term utilities, such as those experienced while receiving a radiologic procedure, a test, or some other short-term treatment. Many tests and treatments have associated noxious as- pects, which, from a patient’s point of view, might be considered somatic/psychologic ‘‘costs’’ (or ‘‘dis- utilities’’) of the tests or treatments. For example, patients who must lie still for extended periods in the confines of a magnetic resonance imaging (MRI) magnet may experience exacerbation of their symp- toms (e.g., a back pain patient) or other manifesta-