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Purpose: The Waiting-Tradeoff (WTO) is an alternative to the chained temporary Time-Tradeoff (TTO) method for short-term health states such as medical testing. It offers a choice between having a potentially noxious test followed by immediate treatment as opposed to waiting for the results of an “ideal” test before having treatment. The result is scaled to a QALY measure using baseline and disease health states for a relevant condition. The WTO was motivated by literature showing the importance of short-term preferences for testing in cost-effectiveness analysis. This study involved the testing of the WTO model by exploring key variables with a sample of healthy subjects who were given scenarios involving testing for atherosclerotic carotid vascular disease with x-ray angiography (XRA) or magnetic resonance angiography (MRA).
Methods: A series of medical scenarios in the context of suspected carotid atherosclerotic vascular disease was constructed by varying three factors of interest: (1) radiologic technology (two levels of invasiveness – MRA and XRA), (2) 3 levels of current health state – severe stroke, transient ischemic attack (TIA), and asymptomatic with abnormal finding; and (3) probability of improvement to asymptomatic (three levels – small, good, and excellent chance). These three different factors lead to 18 possible scenarios that were presented to each of 100 healthy subjects. To ascertain test-retest reliability, each subject repeated the assessment for one randomly selected scenario for each technology.
Results: Means for WTO across subjects ranged from 1.10 to 9.74 days for MRA, and from 8.75 to 30.51 for XRA. Mann-Whitney tests for paired comparisons revealed that WTOs for XRA were significantly larger than WTOs for MRA in all comparisons (p<0.001), indicating subjects preferred the less invasive technology. MRA and XRA waiting times significantly shortened as the current health state increased in severity. Thus, assessments for specific future health states strongly depend on current health states. Regarding test-retest reliability, Spearman’s rho correlation coefficients and intraclass correlation coefficients were 0.634 and 0.603 for MRA, 0.773 and 0.782 for XRA, suggesting adequate reliability.
Conclusions: The results suggest the WTO method is a reliable, valid and useful method for measuring preferences for short-term health states. Additionally, these data suggest dependence of future health state assessment on the current health state. This has important implications for preference measurement over multi-state profiles.
See more of Poster Session - CEA: Methods and Applications; Health Services Research
See more of The 26th Annual Meeting of the Society for Medical Decision Making (October 17-20, 2004)