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Qual Life Res (2010) 19:489497 DOI 10.1007/s11136-010-9605-9
On the (not so) constant proportional trade-off in TTO
Arthur E. Attema Werner B. F. Brouwer
Accepted: 28 January 2010 / Published online: 12 February 2010 The Author(s) 2010. This article is published with open access at Springerlink.com
AbstractPurpose The linear and power QALY models require that people in Time Trade-off (TTO) exercises sacrice the same proportion of lifetime to obtain a health improvement, irrespective of the absolute amount. However, evidence on these constant proportional trade-offs (CPTOs) is mixed, indicating that these versions of the QALY model do not represent preferences. Still, it may be the case that a more general version of the QALY model represents preferences. This version has the property that people want to sacrice the same proportion of utilities of lifetime for a health improvement, irrespective of the amount of this lifetime.
Methods We use a new method to correct TTO scores for utility of life duration and test whether decision makers trade off utility of duration and quality at the same rate irrespective of duration.
Results We nd a robust violation of CPTO for both uncorrected and corrected TTO scores. Remarkably, we nd higher values for longer durations, contrary to most previous studies. This represents the only study correcting for utility of life duration to nd such a violation. Conclusions It seems that the trade-off of life years is indeed not so constantly proportional and, therefore, that health state valuations depend on durations.
Keywords Constant proportional trade-offs
QALY model TTO method Utility of life duration
AbbreviationsQALY Quality-adjusted life yearTTO Time trade-offCPTO Constant proportional trade-offs MET Maximum endurable timeCE Certainty equivalenceFH Full healthD DeathBP Back pain
Introduction
The quality-adjusted life year (QALY) model has become an important model in valuing health benets. To make the model practical, measurement methods are needed in order to elicit the quality of life weights used in this model. One such method is the time trade-off (TTO) method, which is often used to derive (standard) quality of life weights for health states to be used in economic evaluations [1, 2]. The popularity of the TTO, however, cannot be explained by the absence of methodological problems. On the contrary, the TTO has been shown to be prone to several inuences...