| 1. |
- Bleichrodt, Han, et al.
(författare)
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An Experimental Test of a Theoretical Foundation for Rating-scale Valuations
- 1997
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Ingår i: Medical decision making. - : SAGE. - 1552-681X .- 0272-989X. ; 17:2, s. 208-216
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Tidskriftsartikel (refereegranskat)abstract
- A major advantage of using a rating scale in health-utility measurement is its practical applicability: the method is relatively easy to understand, and various health states can be assessed simultaneously. However, a theoretical foundation for rating-scale valuations has not been established. The primary aim of this paper is to present a theoretical foundation for rating-scale valuations based on the theory of measurable value functions and to provide a consistency test to see whether rating-scale valuations do indeed elicit a measurable value function. If rating-scale valuations elicit a measurable value function, then Dyer and Sarin have shown how they are related to von Neumann-Morgenstern (vNM) utilities. The appropriate technique to measure vNM utilities is the standard gamble. Torrance has suggested that rating-scale valuations and standard-gamble valuations are related by a power function. A secondary aim of this paper is to examine the relationship between rating-scale valuations and standard-gamble valuations hypothesized by Torrance. An experiment was designed to test consistency of rating-scale valuations and the relationship between rating-scale valuations and standard-gamble valuations. The experiment tested whether rating-scale valuations are independent of the context in which they are elicited, as they should be if they elicit points on a measurable value function. 80 Swedish and 92 Dutch respondents participated in the experiment. The results showed that rating-scale valuations depend on the number of preferred alternatives in the task and thus violate a basic property of measurable value functions. The estimation of the power function did not result in stable results: parameter estimates varied, in some cases there was indication of misspecification, and in most cases there was indication of heteroskedastic errors. The implications of these findings for the common use of rating-scale valuations in cost-utility analysis are serious: the dependency of the rating-scale valuations on the other health states included in the task casts serious doubts on the validity of the rating-scale method. Key words: QALYs; rating scale; cost-utility analysis; medical decision making. (Med Decis Making 1997;17:208-216))
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| 2. |
- Bleichrodt, Han, et al.
(författare)
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Characterizing QALYs by Risk Neutrality
- 1997
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Ingår i: Journal of Risk and Uncertainty. - : Springer. - 1573-0476 .- 0895-5646. ; 15:2, s. 107-114
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Tidskriftsartikel (refereegranskat)abstract
- This paper shows that QALYs can be derived from more elementary conditions than thought hitherto in the literature: it suffices to impose risk neutrality for life years in every health state. This derivation of QALYs is appealing because it does not require knowledge of concepts from utility theory such as utility independence. Therefore our axiomatization greatly facilitates the assessment of the normative (non)validity of QALYs in medical decision making. Moreover, risk neutrality can easily be tested in experimental designs, which makes it straightforward to assess the descriptive (non)validity of QALYs. Copyright 1997 by Kluwer Academic Publishers
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| 3. |
- Bleichrodt, Han, et al.
(författare)
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Probability Weighting and Utility Curvature in QALY-Based Decision Making
- 1999
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Ingår i: Journal of mathematical psychology. - : Elsevier Inc. - 1096-0880 .- 0022-2496. ; 43:2, s. 238-260
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Tidskriftsartikel (refereegranskat)abstract
- Quality-Adjusted Life-Years (QALYs) are currently the most important utility model in medical decision making. QALYs are calculated by adjusting years of life for the utility of the health state in which these years are spent. For normative reasons the standard gamble is the preferred method to measure health state utilities, but concern exists about its descriptive properties. Recent theoretical work has suggested that probability weighting can explain anomalies in standard gamble measurement. This paper shows that applying probability weighting in standard gamble measurement increases the consistency of QALYs with individual preferences. The consistency of QALYs with individual preferences is not significantly increased further if utility curvature is also taken into account.
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| 4. |
- Bleichrodt, Han, et al.
(författare)
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Standard gamble, time trade-off and rating scale: Experimental results on the ranking properties of QALYs
- 1997
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Ingår i: Journal of health economics. - : Elsevier B.V. - 1879-1646 .- 0167-6296. ; 16:2, s. 155-175
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Tidskriftsartikel (refereegranskat)abstract
- This paper compares the relative performance of quality adjusted life years (QALYs) based on quality weights elicited by rating scale (RS), time trade-off (TTO) and standard gamble (SG). The standard against which relative performance is assessed is individual preference elicited by direct ranking. The correlation between predicted and direct ranking is significantly higher for TTO-QALYs than for RS-QALYs and SG-QALYs. This holds both based on mean Spearman rank correlation coefficients calculated per individual and based on two social choice rules: the method of majority voting and the Borda rule. Undiscounted TTO-QALYs are more consistent with direct ranking than discounted TTO-QALYs.
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| 5. |
- Bleichrodt, Han, et al.
(författare)
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The Validity of QALYs : An Experimental Test of Constant Proportional Tradeoff and Utility Independence
- 1997
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Ingår i: Medical decision making. - 1552-681X .- 0272-989X. ; 17:1, s. 21-32
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Tidskriftsartikel (refereegranskat)abstract
- Pliskin, Shepard, and Weinstein identified three preference conditions that ensure that quality-adjusted life years (QALYs) represent preferences over gambles over chronic health profiles. This paper presents an experimental test of the descriptive validity of two of these preference assumptions: utility independence and constant proportional tradeoff. Eighty students at the Stockholm School of Economics and 92 students at Erasmus University Rotterdam participated in the experiment. The results of the ex periment support the descriptive validity of constant proportional tradeoff: both within groups and between groups constant proportional tradeoff could not be rejected. The results are less supportive of the descriptive validity of utility independence. Within- groups utility independence was rejected. Between-groups utility independence could not be rejected, but this may have been due to a lack of statistical power. Analysis of the individual responses revealed that without adjustment for imprecision of preference, 39 respondents (22.8%) satisfied constant proportional tradeoff. Twenty-three respon dents (13.4%) satisfied utility independence without adjustment for imprecision of pref erence. However, because of the relative unfamiliarity of the respondents with both the health states to be evaluated and the methods of health-state-utility measurement, it is likely that the respondents' preferences were imprecise. Adjusted for imprecision of preference, the upper estimates of the proportions of respondents who satisfied constant proportional tradeoff and utility independence, respectively, were 90.1% (155 respondents) and 75.6% (130 respondents). Pliskin et al. further derived that if an individual's preferences satisfy both constant proportional tradeoff and utility indepen dence, then these preferences can be represented by a more general, risk-adjusted QALY model. Without adjustment for imprecision of preference, ten respondents (5.8%) satisfied both constant proportional tradeoff and utility independence. Adjusted for imprecision of preference, the upper estimate of the proportion of respondents who satisfied both constant proportional tradeoff and utility independence was 68.6% (118 respondents). The results of this study indicate that constant proportional tradeoff holds approximately. The evidence is much weaker for utility independence, however. This has important implications for the use of QALY-type measures in medical decision making. Key words: QALYs; health utility measurements; medical decision making; individual preferences. (Med Decis Making 1996;17:21-32)
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| 6. |
- Bleichrodt, Han, et al.
(författare)
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Time Preference for Health: A Test of Stationarity versus Decreasing Timing Aversion
- 2001
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Ingår i: Journal of mathematical psychology. - : Elsevier Inc. - 1096-0880 .- 0022-2496. ; 45:2, s. 265-282
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Tidskriftsartikel (refereegranskat)abstract
- This paper provides a new and more robust test of the descriptive validity of the constant rate discounted utility model in medical decision analysis. The constant rate discounted utility model is compared with two competing theories, Harvey's (1986) proportional discounting model and Loewenstein and Prelec's (1992) hyperbolic discounting model. To compare the various intertemporal models, previous studies on intertemporal preferences for health assumed a specific parametric form of the utility function for life-years and no discounting within the time periods that health states are experienced. The present study avoids such confounding assumptions by focusing on the axiomatic structure of the discounting models. The present study further differs by using choices instead of matching to elicit intertemporal preferences. The experimental results provide support for decreasing timing aversion, the condition underlying the proportional and the hyperbolic discounting model, but they violate stationarity, the central condition of the constant rate discounted utility model. There is some ambiguity whether the violations of stationarity are primarily caused by an immediacy effect. The results confirm violations of stationarity in choice-based elicitations tasks, in contrast with the results from Ahlbrecht and Weber (1997) which supported stationarity in choices over monetary outcomes.
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