The validity of QALYs: an experimental test of constant proportional tradeoff and utility independence

United States Value Set for the Functional Assessment of Cancer Therapy-General Eight Dimensions (FACT-8D), a Cancer-Specific Preference-Based Quality of Life Instrument

OBJECTIVES

To develop a value set reflecting the United States (US) general population's preferences for health states described by the Functional Assessment of Cancer Therapy (FACT) eight-dimensions preference-based multi-attribute utility instrument (FACT-8D), derived from the FACT-General cancer-specific health-related quality-of-life (HRQL) questionnaire.

METHODS

A US online panel was quota-sampled to achieve a general population sample representative by sex, age (≥ 18 years), race and ethnicity. A discrete choice experiment (DCE) was used to value health states. The valuation task involved choosing between pairs of health states (choice-sets) described by varying levels of the FACT-8D HRQL dimensions and survival (life-years). The DCE included 100 choice-sets; each respondent was randomly allocated 16 choice-sets. Data were analysed using conditional logit regression parameterized to fit the quality-adjusted life-year framework, weighted for sociodemographic variables that were non-representative of the US general population. Preference weights were calculated as the ratio of HRQL-level coefficients to the survival coefficient.

RESULTS

2562 panel members opted in, 2462 (96%) completed at least one choice-set and 2357 (92%) completed 16 choice-sets. Pain and nausea were associated with the largest utility weights, work and sleep had more moderate utility weights, and sadness, worry and support had the smallest utility weights. Within dimensions, more severe HRQL levels were generally associated with larger weights. A preference-weighting algorithm to estimate US utilities from responses to the FACT-General questionnaire was generated. The worst health state's value was -0.33.

CONCLUSIONS

This value set provides US population utilities for health states defined by the FACT-8D for use in evaluating oncology treatments.

The Use of a Discrete Choice Experiment Including Both Duration and Dead for the Development of an EQ-5D-5L Value Set for Australia

BACKGROUND/AIMS

Discrete choice experiments (DCEs) with either duration included an attribute or with dead included as an option can be used as a stand-alone approach to value health states. This paper reports on a DCE with both of these features to develop an EQ-5D-5L value set for Australia.

METHODS

A DCE was undertaken using a large Australian panel of internet respondents, from which a sample of more than 4000 Australian adults was chosen, stratified to be population representative on age and gender. The DCE contained 500 choice triplets, with two EQ-5D-5L health states with duration, and dead as the third option. Each respondent answered 12 choice sets from the 500, stating both the best and worst options from the three available. The design was constructed to estimate a utility algorithm with main effects plus some key interaction terms. A variety of approaches to parameterising interactions, and to anchoring the value set on the required 0-1 scale, were tested. A preferred Australian adult utility algorithm for use in cost-utility analysis was then generated.

RESULTS

In total, 4477 people completed at least one choice set and were included in the analysis. The results reflected the monotonic structure of the EQ-5D-5L, in that moving from no problems to extreme problems led to worsening utility in each dimension. Inclusion of interaction terms demonstrates that the disutility of the first dimension moving to a poor level (defined as either level 5, or level 4 or 5) had a large impact, but subsequent dimensions moving to a poor level had a relatively smaller disutility.

DISCUSSION

This work develops a value set for the EQ-5D-5L in Australia, and also provides a range of methodological insights which can inform future work using a stand-alone DCE to value health in other countries.

Economic evaluation of process utility: elucidating preferences for a non-invasive procedure to treat restenosis

BACKGROUND

In health economic evaluation, utility associated with a health state is outcome-oriented and usually measured using the QALY methodology. Even though there is consistent evidence of utility not only being derived from outcomes but also from procedures, process utility has not been fully integrated in QALY calculations. The aim of this paper is twofold: first, to provide evidence of process utility associated with an alternative treatment to angioplasty, and second, to estimate a monetary value of such process utility using the willingness to pay (WTP) approach.

METHODS

A total of 1514 people were polled on their WTP to avoid angioplasty to have a drug-eluting stent (DES) implanted. WTP is estimated with a contingent valuation (CV) survey. Individuals are also asked if they would be WTP for a non-invasive procedure with similar results being achieved. WTP responses were analyzed using a double bounded (DB) logit model.

RESULTS

Most of the participants showed positive preferences for avoiding angioplasty, with an estimated mean WTP of €5692.87. Using QALY gains for avoiding angioplasty, varying from 0.0035 to 0.08 QALYs, our WTP estimate imply monetary values per QALY that range from €71,160.87 to €1,626,534.28.

DISCUSSION

A WTP of €5692.87 to avoid angioplasty imply a monetary value per QALY that greatly exceed the cost per QALY thresholds established in different countries to consider health programs as beneficial to society. Our results reflect how different methodologies for HTA may lead to different conclusions. From the ICER perspective, the cost that would make the treatment with pills option cost-effective, using a threshold of €40,000/QALY, would be €224. However, a cost-benefit approach could support health programs even with a higher cost.

CONCLUSION

WTP methodology captures outcome and process factors related to angioplasty as our WTP estimations are non-significantly different for the costs of angioplasty. WTP approach must be considered as a genuine alternative to QALY approaches to value process utility.

The Functional Assessment of Cancer Therapy Eight Dimension (FACT-8D), a Multi-Attribute Utility Instrument Derived From the Cancer-Specific FACT-General (FACT-G) Quality of Life Questionnaire: Development and Australian Value Set

OBJECTIVES

To develop a cancer-specific multi-attribute utility instrument derived from the Functional Assessment of Cancer Therapy - General (FACT-G) health-related quality of life (HRQL) questionnaire.

METHODS

We derived a descriptive system based on a subset of the 27-item FACT-G. Item selection was informed by psychometric analyses of existing FACT-G data (n = 6912) and by patient input (n = 82). We then conducted an online valuation survey, with participants recruited via an Australian general population online panel. A discrete choice experiment (DCE) was used, with attributes being the HRQL dimensions of the descriptive system and survival duration, and 16 choice-pairs per participant. Utility decrements were estimated with conditional logit and mixed logit modeling.

RESULTS

Eight HRQL dimensions were included in the descriptive system: pain, fatigue, nausea, sleep, work, social support, sadness, and future health worry; each with 5 levels. Of 1737 panel members who accessed the valuation survey, 1644 (95%) completed 1 or more DCE choice-pairs and were included in analyses. Utility decrements were generally monotonic; within each dimension, poorer HRQL levels generally had larger utility decrements. The largest utility decrements were for the highest levels of pain (-0.40) and nausea (-0.28). The worst health state had a utility of -0.54, considerably worse than dead.

CONCLUSIONS

A descriptive system and preference-based scoring approach were developed for the FACT-8D, a new cancer-specific multi-attribute utility instrument derived from the FACT-G. The Australian value set is the first of a series of country-specific value sets planned that can facilitate cost-utility analyses based on items from the FACT-G and related FACIT questionnaires containing FACT-G items.

A Head-to-Head Comparison of the Standard Quality-Adjusted Life Year Model With the Annual Profile Model

OBJECTIVES

The standard quality-adjusted life year (QALY) model (SQM) assumes time-utility independence within constant health states and additive independence when health varies over time. The validity of SQM has been challenged through reported violations of these assumptions. An alternative approach that relaxes these assumptions is to assign a single valuation to an entire health profile: an integral assessment of disease severity over time. Here, we compare SQM with the annual profile model (APM) and test SQM for additive independence.

METHODS

Eighty-two respondents valued 6 episodic conditions, including 4 of short duration, with SQM and APM, using the time trade-off method. Inter-rater reliability was assessed using intraclass correlation coefficients. Face validity was tested by asking respondents how well they were able to imagine the health states under SQM and APM. We calculated SQM QALY values for a 1-year time period, allowing for a direct comparison with APM values. For the short-term conditions we expected higher QALY values for SQM, violating additive independence.

RESULTS

APM showed higher interrater reliability (intraclass correlation coefficient of 0.53 vs 0.18, respectively) and better face validity than SQM, with 6% (APM) vs 21% (SQM) of all respondents reporting difficulties. Additive independence of SQM was violated in 5 of the 6 conditions (including the 4 short duration health states), with higher QALY values under SQM (mean difference 0.04).

CONCLUSION

The impact of short-term conditions is systematically underestimated under SQM when compared to a health profile model. APM is a less restrictive model and demonstrates better validity.

An overview of the time trade-off method: concept, foundation, and the evaluation of distorting factors in putting a value on health

INTRODUCTION

Preference-based instruments measuring health status express the value of specific health states in a single number. One method used is time trade-off (TTO). Health-status values are key elements in calculating quality-adjusted life years (QALYs) and are pertinent for resource allocation. Since they are used in economic evaluations of healthcare, searching for a theoretical foundation of TTO in economics is justified.

AREA COVERED

This paper provides an overview of TTO, including its relation to economic theory, and discusses biases and distortions, compiled from recent and older research. Inconsistencies between TTO and random utility theory were detected; The TTO is confounded by time preferences and by respondents' life expectancies. TTO is cognitively challenging, therefore guidance during the interviews is needed, producing interview effects. TTO does not measure one thing at a time, nor are the values independent of other states that are being valued in the same task. That is, TTO does not exhibit theoretical measurement properties such as unidimensionality and the invariance principle.

EXPERT OPINION

We conclude that the TTO may be a pragmatic method of eliciting health state values, but the limitations in regard to measurement theory and practical elicitation problems makes it prone to inconsistencies and arbitrariness.

Health state utilities associated with treatment for transfusion-dependent β-thalassemia

OBJECTIVES

Transfusion-dependent β-thalassemia (TDT) is a genetic disease that affects production of red blood cells. Conventional treatment involves regular red blood cell transfusions and iron chelation, which has a substantial impact on quality of life. While potentially curative, allogeneic hematopoietic stem cell transplantation (allo-HSCT) is associated with risk of complications, including graft-versus-host disease (GvHD). Gene addition therapy, a novel treatment approach, involves autologous transplantation of the patient's own genetically modified hematopoietic stem cells. The purpose of this study was to estimate utilities associated with treatment approaches for TDT.

METHODS

General population respondents in England valued eight health state vignettes (developed with clinician, patient, and parent input) in time trade-off interviews.

RESULTS

A total of 207 participants completed interviews (49.8% female; mean age = 43.2 years). Mean (SD) utilities for the pre-transplant health states were 0.73 (0.25) with oral chelation and 0.63 (0.32) with subcutaneous chelation. Mean utilities for the transplant year were 0.62 (0.35) for gene addition therapy, 0.47 (0.39) for allo-HSCT, and 0.39 (0.39) for allo-HSCT with acute GvHD. Post-transplant utilities were 0.93 (0.15) for transfusion independent, 0.75 (0.25) for 60% transfusion reduction, and 0.51 (0.38) for chronic GvHD. Acute and chronic GvHD were associated with significant disutility (acute = - 0.09, p < 0.0001; chronic = - 0.42, p < 0.0001).

CONCLUSIONS

Utilities followed expected patterns, with logical differences between treatment options for TDT and substantially greater utility for transfusion independence than for ongoing treatment involving transfusion and chelation. These utilities may be useful in cost-utility models estimating the value of treatments for TDT.

U.K. utility weights for the EORTC QLU-C10D

The EORTC QLU-C10D is a new multi-attribute utility instrument derived from the widely used cancer-specific quality of life questionnaire, EORTC QLQ-C30. It contains 10 dimensions (physical functioning, role functioning, social functioning, emotional functioning, pain, fatigue, sleep, appetite, nausea, bowel problems), each with four levels. The aim of this study was to provide U.K. general population utility weights for the QLU-C10D. A U.K. online panel was quota-sampled to align the sample to the general population proportions of sex and age (≥18 years). The online valuation survey included a discrete choice experiment (DCE). Each participant was asked to complete 16 choice-pairs, each comprising two QLU-C10D health states plus duration. DCE data were analysed using conditional logistic regression to generate utility weights. Data from 2,187 respondents who completed at least one choice set were included in the DCE analysis. The final U.K. QLU-C10D utility weights comprised decrements for each level of each health dimension. For nine of the 10 dimensions (all except appetite), the expected monotonic pattern was observed across levels: Utility decreased as severity increased. For the final model, consistent monotonicity was achieved by merging inconsistent adjacent levels for appetite. The largest utility decrements were associated with physical functioning and pain. The worst possible health state (the worst level of each dimension) is -0.083, which is considered slightly worse than being dead. The U.K.-specific utility weights will enable cost-utility analysis (CUA) for the economic evaluation of new oncology therapies and technologies in the United Kingdom, where CUA is commonly used to inform resource allocation.

Influence of elicitation procedure and phrasing on health state valuations in experience-based time trade-off tasks among diabetes patients in China

Purpose

Open-ended and iteration-based time trade-off (TTO) tasks can both be used for valuation of health states. It has so far not been examined how the elicitation procedure affects the valuation of experience-based health states. The purpose of this study is to investigate the influence of elicitation procedure on experience-based health state values elicited by the TTO method.

Methods

156 Chinese adults with type 2 diabetes participated in face-to-face interviews with an open-ended or an iteration-based TTO task. The association between the type of TTO task and the valuation of health states was investigated through multiple linear regression analyses. A modified open-ended TTO task was also developed (n = 33) to test whether different phrasings of open-ended TTO tasks influence TTO values.

Results

Higher TTO values were observed in the original open-ended TTO task compared to the iteration-based task, which indicates that the elicitation procedure influences the valuation of health states. When the modified open-ended task was introduced, the difference between the two elicitation procedures was no longer statistically significant, suggesting that the phrasing and/or visual presentation of the TTO task may influence the valuation of health states.

Conclusions

The choice of elicitation procedure as well as the description of experience-based TTO tasks may influence the valuation of health states. Further research is warranted, also in other cultural contexts, to further explore these findings.

Do time trade-off values fully capture attitudes that are relevant to health-related choices?

Previous research has shown that demographics, beliefs, and self-reported own health influence TTO values. Our hypothesis is that attitudes towards length and quality of life influence TTO values, but should no longer affect a set of related choices that are based on respondents' own TTO scores. A representative sample of 1339 respondents was asked their level of agreement to four statements relating to the importance of quality and length of life. Respondents then went on to value 4 EQ-5D 5L states using an online interactive survey and a related set of 6 pairwise health-related choice questions, set up, so that respondents should be indifferent between choice options. We explored the impact of attitudes using regression analysis for TTO values and a logit model for choices. TTO values were correlated with the attitudes and were found to have a residual impact on the choices. In particular, those respondents who preferred quality of life over length of life gave less weight to the differences in years and more weight to differences in quality of life in these choice. We conclude that although the TTO responses reflect attitudes, these attitudes continue to affect health-related choices.

Australian Utility Weights for the EORTC QLU-C10D, a Multi-Attribute Utility Instrument Derived from the Cancer-Specific Quality of Life Questionnaire, EORTC QLQ-C30

BACKGROUND

The EORTC QLU-C10D is a new multi-attribute utility instrument derived from the widely used cancer-specific quality-of-life (QOL) questionnaire, EORTC QLQ-C30. The QLU-C10D contains ten dimensions (Physical, Role, Social and Emotional Functioning; Pain, Fatigue, Sleep, Appetite, Nausea, Bowel Problems), each with four levels. To be used in cost-utility analysis, country-specific valuation sets are required.

OBJECTIVE

The aim of this study was to provide Australian utility weights for the QLU-C10D.

METHODS

An Australian online panel was quota-sampled to ensure population representativeness by sex and age (≥ 18 years). Participants completed a discrete choice experiment (DCE) consisting of 16 choice-pairs. Each pair comprised two QLU-C10D health states plus life expectancy. Data were analysed using conditional logistic regression, parameterised to fit the quality-adjusted life-year framework. Utility weights were calculated as the ratio of each QOL dimension-level coefficient to the coefficient on life expectancy.

RESULTS

A total of 1979 panel members opted in, 1904 (96%) completed at least one choice-pair, and 1846 (93%) completed all 16 choice-pairs. Dimension weights were generally monotonic: poorer levels within each dimension were generally associated with greater utility decrements. The dimensions that impacted most on choice were, in order, Physical Functioning, Pain, Role Functioning and Emotional Functioning. Oncology-relevant dimensions with moderate impact were Nausea and Bowel Problems. Fatigue, Trouble Sleeping and Appetite had relatively small impact. The value of the worst health state was -0.096, somewhat worse than death.

CONCLUSIONS

This study provides the first country-specific value set for the QLU-C10D, which can facilitate cost-utility analyses when applied to data collected with the EORTC QLQ-C30, prospectively and retrospectively.

The QALY Model and Individual Preferences for Health States and Health Profiles over Time: A Systematic Review of the Literature

The numbers of quality-adjusted life years (QALYs) gained are increasingly being used to represent the gains in individual utility from treatment. This requires that the value of a health improvement to an individual is a simple product of gains in quality of life and length of life. The article reports on a systematic review of the literature on 2 issues: whether the value of a state is affected by how long the state lasts, and by states that come before or after it. It was found that individual preferences over health are influenced by the duration of health states and their sequence. However, although there is much variation across individual respondents, the assumptions tend to hold much better when valuations are aggregated across respondents, which is encouraging for economic evaluations that rely on using average (mean or median) values.

The DEP-6D, a new preference-based measure to assess health states of dependency

In medical literature there are numerous multidimensional scales to measure health states for dependence in activities of daily living. However, these scales are not preference-based and are not able to yield QALYs. On the contrary, the generic preference-based measures are not sensitive enough to measure changes in dependence states. The objective of this paper is to propose a new dependency health state classification system, called DEP-6D, and to estimate its value set in such a way that it can be used in QALY calculations. DEP-6D states are described as a combination of 6 attributes (eat, incontinence, personal care, mobility, housework and cognition problems), with 3-4 levels each. A sample of 312 Spanish citizens was surveyed in 2011 to estimate the DEP-6D preference-scoring algorithm. Each respondent valued six out of the 24 states using time trade-off questions. After excluding those respondents who made two or more inconsistencies (6% out of the sample), each state was valued between 66 and 77 times. The responses present a high internal and external consistency. A random effect model accounting for main effects was the preferred model to estimate the scoring algorithm. The DEP-6D describes, in general, more severe problems than those usually described by means of generic preference-based measures. The minimum score predicted by the DEP-6D algorithm is -0.84, which is considerably lower than the minimum value predicted by the EQ-5D and SF-6D algorithms. The DEP-6D value set is based on community preferences. Therefore it is consistent with the so-called 'societal perspective'. Moreover, DEP-6D preference weights can be used in QALY calculations and cost-utility analysis.

Response Patterns in Health State Valuation Using Endogenous Attribute Attendance and Latent Class Analysis

Not accounting for simplifying decision-making heuristics when modelling data from discrete choice experiments has been shown potentially to lead to biased inferences. This study considers two ways of exploring the presence of attribute non-attendance (that is, respondents considering only a subset of the attributes that define the choice options) in a health state valuation discrete choice experiment. The methods used include the latent class (LC) and endogenous attribute attendance (EAA) models, which both required adjustment to reflect the structure of the quality-adjusted life year (QALY) framework for valuing health outcomes. We find that explicit consideration of attendance patterns substantially improves model fit. The impact of allowing for non-attendance on the estimated QALY weights is dependent on the assumed source of non-attendance. If non-attendance is interpreted as a form of preference heterogeneity, then the inferences from the LC and EAA models are similar to those from standard models, while if respondents ignore attributes to simplify the choice task, the QALY weights differ from those using the standard approach. Because the cause of non-attendance is unknown in the absence of additional data, a policymaker may use the range of weights implied by the two approaches to conduct a sensitivity analysis.

Using a discrete choice experiment to value the QLU-C10D: feasibility and sensitivity to presentation format

PURPOSE

To assess the feasibility of using a discrete choice experiment (DCE) to value health states within the QLU-C10D, a utility instrument derived from the QLQ-C30, and to assess clarity, difficulty, and respondent preference between two presentation formats.

METHODS

We ran a DCE valuation task in an online panel (N = 430). Respondents answered 16 choice pairs; in half of these, differences between dimensions were highlighted, and in the remainder, common dimensions were described in text and differing attributes were tabulated. To simplify the cognitive task, only four of the QLU-C10D's ten dimensions differed per choice set. We assessed difficulty and clarity of the valuation task with Likert-type scales, and respondents were asked which format they preferred. We analysed the DCE data by format with a conditional logit model and used Chi-squared tests to compare other responses by format. Semi-structured telephone interviews (N = 8) explored respondents' cognitive approaches to the valuation task.

RESULTS

Four hundred and forty-nine individuals were recruited, 430 completed at least one choice set, and 422/449 (94 %) completed all 16 choice sets. Interviews revealed that respondents found ten domains difficult but manageable, many adopting simplifying heuristics. Results for clarity and difficulty were identical between formats, but the "highlight" format was preferred by 68 % of respondents. Conditional logit parameter estimates were monotonic within domains, suggesting respondents were able to complete the DCE sensibly, yielding valid results.

CONCLUSION

A DCE valuation task in which only four of the QLU-C10D's ten dimensions differed in any choice set is feasible for deriving utility weights for the QLU-C10D.

Estimating health state utility values from discrete choice experiments--a QALY space model approach

Using discrete choice experiments (DCEs) to estimate health state utility values has become an important alternative to the conventional methods of Time Trade-Off and Standard Gamble. Studies using DCEs have typically used the conditional logit to estimate the underlying utility function. The conditional logit is known for several limitations. In this paper, we propose two types of models based on the mixed logit: one using preference space and the other using quality-adjusted life year (QALY) space, a concept adapted from the willingness-to-pay literature. These methods are applied to a dataset collected using the EQ-5D. The results showcase the advantages of using QALY space and demonstrate that the preferred QALY space model provides lower estimates of the utility values than the conditional logit, with the divergence increasing with worsening health states.

Comparison of contemporaneous EQ-5D and SF-6D responses using scoring algorithms derived from similar valuation exercises

OBJECTIVES

Poor agreement between preference-based health-related quality-of-life instruments has been widely reported across patient and community-based samples. This study compares index scores generated from contemporaneous EQ-5D (3-level version) and SF-6D (SF-36 version) responses using scoring algorithms derived from independently-conducted Australian population-representative discrete choice experiments (DCEs), providing the first comparative analysis of health state valuations using the same method of valuation across the full value sets.

METHODS

EQ-5D and SF-6D responses from seven patient data sets were transformed into health state valuations using published DCE-derived scoring algorithms. The empirical comparative evaluation consisted of graphical illustration of the location and spread of index scores, reporting of basic descriptive statistics, exploration of between-measure differences in mean index scores, and analysis of agreement.

RESULTS

Compared with previously published findings regarding the comparability of "conventional" EQ-5D and SF-6D index scores, health state valuations from the DCE-derived scoring procedures showed that agreement between scores remained "fair" (intraclass correlation coefficient values across the seven data sets ranged from 0.375 to 0.615). Mean SF-6D scores were significantly lower than the respective mean EQ-5D score across all patient groups (mean difference for the whole sample = 0.253).

CONCLUSIONS

The magnitude of disagreement previously reported between EQ-5D and SF-6D index scores is not ameliorated through the application of DCE-derived value sets; sizeable discrepancies remain. These findings suggest that differences between EQ-5D and SF-6D index scores persist because of their respective descriptive systems. Further research is required to explore the implications of variations in the descriptive systems of preference-based instruments.

An Australian discrete choice experiment to value eq-5d health states

Conventionally, generic quality-of-life health states, defined within multi-attribute utility instruments, have been valued using a Standard Gamble or a Time Trade-Off. Both are grounded in expected utility theory but impose strong assumptions about the form of the utility function. Preference elicitation tasks for both are complicated, limiting the number of health states that each respondent can value and, therefore, that can be valued overall. The usual approach has been to value a set of the possible health states and impute values for the remainder. Discrete Choice Experiments (DCEs) offer an attractive alternative, allowing investigation of more flexible specifications of the utility function and greater coverage of the response surface. We designed a DCE to obtain values for EQ-5D health states and implemented it in an Australia-representative online panel (n = 1,031). A range of specifications investigating non-linear preferences with respect to time and interactions between EQ-5D levels were estimated using a random-effects probit model. The results provide empirical support for a flexible utility function, including at least some two-factor interactions. We then constructed a preference index such that full health and death were valued at 1 and 0, respectively, to provide a DCE-based algorithm for Australian cost-utility analyses.

Quality-of-life-adjusted hazard of death: a formulation of the quality-adjusted life-years model of use in benefit-risk assessment

BACKGROUND

Although the quality-adjusted life-years (QALY) model is standard in health technology assessment, quantitative methods are less frequent but increasingly used for benefit-risk assessment (BRA) at earlier stages of drug development. A frequent challenge when implementing metrics for BRA is to weigh the importance of effects on a chronic condition against the risk of severe events during the trial. The lifetime component of the QALY model has a counterpart in the BRA context, namely, the risk of dying during the study.

METHODS

A new concept is presented, the hazard of death function that a subject is willing to accept instead of the baseline hazard to improve his or her chronic health status, which we have called the quality-of-life-adjusted hazard of death.

RESULTS

It has been proven that if assumptions of the linear QALY model hold, the excess mortality rate tolerated by a subject for a chronic health improvement is inversely proportional to the mean residual life.

CONCLUSIONS

This result leads to a new representation of the linear QALY model in terms of hazard rate functions and allows utilities obtained by using standard methods involving trade-offs of life duration to be translated into thresholds of tolerated mortality risk during a short period of time, thereby avoiding direct trade-offs using small probabilities of events during the study, which is known to lead to bias and variability.

Magnetic resonance neurography research: evaluation of its effectiveness

Magnetic resonance neurography (MRN) is a specialized technique that is rapidly becoming part of the diagnostic algorithm of peripheral nerve pathology. However, in order for this modality to be considered appropriate, its value compared with current methods of diagnosis should be established. Therefore, radiologists involved in MRN research should use appropriate methodology to evaluate MRN's effectiveness with a multidisciplinary approach. This article reviews the various tiers of research available to assess the clinical value of a diagnostic modality with an emphasis on how to evaluate the impact of MRN on diagnostic thinking and therapeutic decisions.

Valuing SF-6D Health States Using a Discrete Choice Experiment

BACKGROUND

SF-6D utility weights are conventionally produced using a standard gamble (SG). SG-derived weights consistently demonstrate a floor effect not observed with other elicitation techniques. Recent advances in discrete choice methods have allowed estimation of utility weights. The objective was to produce Australian utility weights for the SF-6D and to explore the application of discrete choice experiment (DCE) methods in this context. We hypothesized that weights derived using this method would reflect the largely monotonic construction of the SF-6D.

METHODS

We designed an online DCE and administered it to an Australia-representative online panel (n = 1017). A range of specifications investigating nonlinear preferences with respect to additional life expectancy were estimated using a random-effects probit model. The preferred model was then used to estimate a preference index such that full health and death were valued at 1 and 0, respectively, to provide an algorithm for Australian cost-utility analyses.

RESULTS

Physical functioning, pain, mental health, and vitality were the largest drivers of utility weights. Combining levels to remove illogical orderings did not lead to a poorer model fit. Relative to international SG-derived weights, the range of utility weights was larger with 5% of health states valued below zero.

CONCLUSION

s. DCEs can be used to investigate preferences for health profiles and to estimate utility weights for multi-attribute utility instruments. Australian cost-utility analyses can now use domestic SF-6D weights. The comparability of DCE results to those using other elicitation methods for estimating utility weights for quality-adjusted life-year calculations should be further investigated.

Probabilistic choice models in health-state valuation research: background, theories, assumptions and applications

Interest is rising in measuring subjective health outcomes, such as treatment outcomes that are not directly quantifiable (functional disability, symptoms, complaints, side effects and health-related quality of life). Health economists in particular have applied probabilistic choice models in the area of health evaluation. They increasingly use discrete choice models based on random utility theory to derive values for healthcare goods or services. Recent attempts have been made to use discrete choice models as an alternative method to derive values for health states. In this article, various probabilistic choice models are described according to their underlying theory. A historical overview traces their development and applications in diverse fields. The discussion highlights some theoretical and technical aspects of the choice models and their similarity and dissimilarity. The objective of the article is to elucidate the position of each model and their applications for health-state valuation.

Efficiency and equity: a stated preference approach

Outcome measurement in the economic evaluation of health care considers outcomes independent of to whom they accrue. This article reports on a discrete choice experiment designed to elicit population preferences regarding the allocation of health gain between hypothetical groups of potential patients. A random-effects probit model is estimated, and a technique for converting these results into equity weights for use in economic evaluation is adopted. On average, the modelling predicts a relatively high social value on health gains accruing to nonsmokers, carers, those with a low income and those with an expected age of death less than 45 years. Respondents tend to favour individuals with similar characteristics to themselves. These results challenge the conventional practice of assuming constant equity weighting. For decision makers, whether a formal equity weighting system represents an improvement on more informal approaches to weighing up equity and efficiency concerns remains uncertain.

Lead time TTO: leading to better health state valuations?

Preference elicitation tasks for better than dead (BTD) and worse than dead (WTD) health states vary in the conventional time trade-off (TTO) procedure, casting doubt on uniformity of scale. 'Lead time TTO' (LT-TTO) was recently introduced to overcome the problem. We tested different specifications of LT-TTO in comparison with TTO in a within-subject design. We elicited preferences for six health states and employed an intertemporal ranking task as a benchmark to test the validity of the two methods. We also tested constant proportional trade-offs (CPTO), while correcting for discounting, and the effect of extending the lead time if a health state is considered substantially WTD. LT-TTO produced lower values for BTD states and higher values for WTD states. The validity of CPTO varied across tasks, but it was higher for LT-TTO than for TTO. Results indicate that the ratio of lead time to disease time has a greater impact on results than the total duration of the time frame. The intertemporal ranking task could not discriminate between TTO and LT-TTO.

The impact of patients' subjective life expectancy on time tradeoff valuations

BACKGROUND

Quality-adjusted life-year (QALY) calculations in economic evaluations are typically based on general public or patient health state valuations elicited with the time tradeoff method (TTO). Such health state valuations elicited among the general public have been shown to be affected by respondents' subjective life expectancy (SLE). This suggests that TTO exercises based on time frames other than SLE may lead to biased estimates. It has not yet been investigated whether SLE also affects patient valuations.

OBJECTIVE

To empirically investigate whether patients' SLE affects TTO valuations of their current health state.

METHODS

Patients with different severities of diabetic retinopathy were asked in a telephone interview to value their own health status using TTO. The TTO time frame (t) presented was based on age- and sex-dependent actuarial life expectancy. Patients were then asked to state their SLE. Simple and multiple regression techniques were used to assess the effect of the patients' SLE on their TTO responses.

RESULTS

In total, 145 patients completed the telephone interview. Patients' TTO values were significantly influenced by their SLE. The TTO value decreased linearly with every additional year of difference between t and the patients' SLE; that is, patients were more willing to give up years the shorter their SLE compared with t.

CONCLUSION

Patients' SLE influenced their TTO valuations, suggesting that respondents' SLE may be the most appropriate time frame to use in TTO exercises in patients. The use of other time periods may bias the TTO valuations, as the respondents may experience the presented time frame as a gain or a loss. The effect seems to be larger in patient valuations than in general public valuations.

The way that you do it? An elaborate test of procedural invariance of TTO, using a choice-based design

The time tradeoff (TTO) method is often used to derive Quality-Adjusted Life Year health state valuations. An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences. In particular, fixing the duration in the health state to be valued and inferring the duration in full health that renders an individual indifferent, causes valuations to be higher than when the duration in full health is fixed and the duration in the health state to be valued is elicited. This paper presents a new test of procedural invariance for a broad range of time horizons, while using a choice-based design and adjusting for discounting. As one of the known problems with the conventional procedure is the violation of constant proportional tradeoffs (CPTO), we also investigate CPTO for the alternative TTO procedure. Our findings concerning procedural invariance are rather supportive for the TTO procedure. We find no violations of procedural invariance except for the shortest gauge duration. The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

Is the QALY blind, deaf and dumb to equity? NICE's considerations over equity

INTRODUCTION/BACKGROUND

The quality-adjusted life year (QALY) is the preferred measure of health outcome used to inform decisions over the use of health care interventions in the UK NHS. This measure considers the overall impact of alternative interventions on both the quantity and quality of life.

SOURCES OF DATA

Review of the relevant literature. Areas of agreement The QALY assumes that health improvement is equally valued between individuals. Areas of controversy Some can perceive as equitable, that is fair, the assumption that health improvement is equally valued between individuals in the QALY. However, others may believe that this assumption leaves no space for alternative views over equity to be explicitly considered in societal decision making.

GROWING POINTS

The role of equity in decision making in the UK has been subject of intense debate, and controversy, and to-date there is no consensus on whether, or how, should NICE should change their general process.

AREAS TIMELY FOR DEVELOPING RESEARCH

Further examination of the issues needs to be debated and researched.

A test of independence of discounting from quality of life

The quality-adjusted life-years (QALY) model assumes quality and quantity of life can be multiplied into a single index and requires quality and quantity to be mutually independent, which need not hold empirically. This paper proposes a new test for measuring independence of utility of life duration from quality of life in a riskless setting. We use a large representative sample of Dutch citizens and include two health states generally considered better than dead (BTD) and one health state considered worse than dead (WTD). Independence cannot be rejected when comparing the BTD health states, but is rejected when comparing the BTD states with the WTD state. In particular, utility of life duration becomes more concave for the WTD state. This may suggest that independence holds only for BTD health states. This has implications for the QALY model and would require using sign-dependent utility of life duration functions.

Constantly proving the opposite? A test of CPTO using a broad time horizon and correcting for discounting

Purpose

An important assumption underlying the quality-adjusted life year (QALY) model is that people trade off life years against health in the same proportion irrespective of the number of remaining life years. This is known as the constant proportional trade-offs (CPTO) condition. Previous studies have produced mixed empirical evidence about the validity of CPTO. This paper is the first to test CPTO using the time trade-off (TTO) method for a broad time horizon.

Methods

In a sample of 83 students, we use a choice based TTO protocol to elicit TTO scores for back pain, using ten different gauge durations ranging between 1 and 46 years. The TTO scores are corrected for discounting, which is elicited by means of the direct method.

Results

We find average TTO scores varying between 0.72 and 0.81. Although the scores do not differ much for different durations in absolute terms, some differences are significant, rejecting CPTO, with and without correcting for discounting. No clear relationship between TTO scores and gauge duration is found. An anchoring and rounding heuristic to some extent explains our results.

Conclusions

Our findings highlight the importance of elicitation methods and context dependencies in QALY measurement and warrant detailed investigation of their influence.

On the (not so) constant proportional trade-off in TTO

Purpose

The linear and power QALY models require that people in Time Trade-off (TTO) exercises sacrifice 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 sacrifice 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 find a robust violation of CPTO for both uncorrected and corrected TTO scores. Remarkably, we find higher values for longer durations, contrary to most previous studies. This represents the only study correcting for utility of life duration to find 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.

Measuring the quality-of-life effects of diagnostic and screening tests

Health-related quality of life (HRQL) is a central concept for understanding the outcomes of medical care. When used in cost-effectiveness analysis, HRQL is typically measured for conditions persisting over long time frames (years), and quality-adjusted life year (QALY) values are generated. Consequently, years are the basic unit of time for cost-effectiveness analysis results: dollars spent per QALY gained. However, shorter term components of health care may also affect HRQL, and there is increased interest in measuring and accounting for these events. In radiology, the short-term HRQL effects of screening and diagnostic testing may affect a test's cost-effectiveness, even though they may only last for days. The unique challenge in radiology HRQL assessment is to realistically tap into the testing and screening experience while remaining consistent with QALY theory. The authors review HRQL assessment and highlight methods developed to specifically address the short-term effects of radiologic screening and testing.

Methods for measuring temporary health States for cost-utility analyses

A variety of methods are available to measure preferences for temporary health states for cost-utility analyses. The objectives of this review were to summarize the available temporary health-state valuation methods, identify advantages and disadvantages of each, and identify areas for future research. We describe the key aspects of each method and summarize advantages and disadvantages of each method in terms of consistency with QALY theory, relevance to temporary health-state-specific domains, ease of use, time preference, and performance in validation studies. Two broad categories of methods were identified: traditional and adapted. Traditional methods were health status instruments, time trade-off (TTO), and the standard gamble (SG). Methods adapted specifically for temporary health-state valuation were TTO with specified duration of the health state, TTO with a lifespan modification, waiting trade-off, chained approaches for TTO and SG, and sleep trade-off. Advantages and disadvantages vary by method and no 'gold standard' method emerged. Selection of a method to value temporary health states will depend on the relative importance of the following considerations: ability to accurately capture the unique characteristics of the temporary health state, level of respondent burden and cognition, theoretical consistency of elicited preference values with the overall purpose of the study, and resources available for study development and data collection. Further research should focus on evaluating validity, reliability and feasibility of temporary health-state valuation methods.

A note on the nature of utility in time and health and implications for cost utility analysis

Time Trade-Off (TTO) valuations of health are widely used in economic evaluation of health care. Current approaches to eliciting TTO values, and their use in economic evaluation, rest on specific assumptions about the way utility relates to time and health. Both the assumptions themselves and evidence of violations of them are discussed in the literature - yet the issues appear not to be widely appreciated by those using and applying TTO in economic evaluation. This paper adds to that literature by demonstrating both the requirements of TTO and violations of these assumptions in terms of the underlying indifference curve maps and utility functions. The advantage of this approach is that it demonstrates very clearly a number of fundamental problems for the way TTO values are currently elicited and used in cost utility analysis. In essence, it is extremely unwise to assume that the current 'tariffs' of TTO values, such as those widely used in cost utility analysis to inform health sector decisions in many countries can be applied irrespective of the duration of the health states to which they are assigned. The estimates of QALYs that result will, quite often, simply be wrong. We conclude by pointing to a number of possible solutions.

Do individuals consider expected income when valuing health states?

Objectives:The purpose of this study was to empirically explore whether individuals take their expected income into consideration when directly valuing predefined health states. This was intended to help determine how to handle productivity costs due to morbidity in a cost-effectiveness analysis.

Methods:Two hundred students each valued four hypothetical health states by using time trade-off (TTO) and a visual analogue scale (VAS). The students were randomly assigned to two groups. One group was simply asked, without mentioning income, to value the different health states (the non-income group). The other group was explicitly asked to consider their expected income in relation to the health states in their valuations (the income group).

Results:For health states that are usually assumed to have a large effect on income, the valuations made by the income group seemed to be lower than the valuations made by the non-income group. Among the students in the non-income group, 96 percent stated that they had not thought about their expected income when they valued the health states. In the income group, 40 percent believed that their expected income had affected their valuations of the health states.

Conclusion:The results show that, as long as income is not mentioned, most individuals do not seem to consider their expected income when they value health states. This indicates that productivity costs due to morbidity are not captured within individuals' health state valuations. These findings, therefore, suggest that productivity costs due to morbidity should be included as a cost in cost-effectiveness analyses.

New tests of QALYs when health varies over time

This paper performs new tests of the QALY model when health varies over time. Our tests do not involve confounding assumptions and are robust to violations of expected utility. The results support the use of QALYs at the aggregate level, i.e. in economic evaluations of health care. At the individual level, there is less support for QALYs. The individual data are, however, largely consistent with a more general QALY-type model that remains tractable for applications.

The Cost of Uncertain Life Span

A considerable amount of uncertainty surrounds the length of human life. The standard deviation in adult life span is about 15 years in the U.S., and theory and evidence suggest it is costly. I calibrate a utility-theoretic model of preferences over length of life and show that one fewer year in standard deviation is worth about half a mean life year. Differences in the standard deviation exacerbate cross-sectional differences in life expectancy between the U.S. and other industrialized countries, between rich and poor countries, and among poor countries. Accounting for the cost of life-span variance also appears to amplify recently discovered patterns of convergence in world average human well-being. This is partly for methodological reasons and partly because unconditional variance in human length of life, primarily the component due to infant mortality, has exhibited even more convergence than life expectancy.

Thurstone scaling as a measurement method to quantify subjective health outcomes

BACKGROUND

Many objective health outcome measures are used to monitor patients or evaluate health interventions, but there are also subjective measures. For the latter, it is difficult to derive metric data, which are needed to quantify health outcomes such as functional disability, severity of side effects, and health status.

OBJECTIVE

Thurstone's Law of Comparative Judgment is presented as an alternative means to derive metric values for subjective health outcomes. The appeal of Thurstone's scaling model is that it can transform subjective individual rank order data or comparative preference data to a single group composite interval scale. To demonstrate its contribution, an empirical study was conducted, focusing on the valuation of health states.

RESEARCH DESIGN

Rank order data were collected for 18 health states and were then used as input for Thurstone scaling. Visual analogue scale (VAS) values were also collected for the same states.

SUBJECTS

An agency for market research recruited 212 Dutch respondents aged 18-75 years.

RESULTS

The derived Thurstone values showed a strong relationship with the VAS values. The positions of the 2 worst states were almost identical on the VAS and the Thurstone scale. Intermediate states were scaled somewhat differently by the 2 methods.

CONCLUSIONS

For many subjective health outcomes, Thurstone scaling and its derivatives may be an attractive methodology to arrive at quantitative measures.

Feasibility and Reliability of the Annual Profile Method for Deriving QALYs for Short-Term Health Conditions

Introduction . When health varies over time, the standard quality-adjusted life year model operates under the assumptions of time utility independence within each health state and additive independence between health states. These assumptions can be relaxed by an integral assessment of disease severity over time. The authors present the annual profile method (APM), which values health profiles on a 1-year base, and test the APM for feasibility, consistency, and test-retest reliability. Methods . A population panel, general practitioners, medical advisers, and a panel of the Dutch Consumers Association valued vignettes for 46 disease stages using the visual analog scale (VAS) and time tradeoff (TTO) methods. Vignettes contained disease-specific information, a generic description (EQ-6D5L), a description of the disease course over time, and a visual representation of the disease. Feasibility was tested by missing and inconsistent responses. Consistency between and within panels was tested with a generalizability study, analysis of variance, and standard correlation coefficients. Test-retest reliability was tested with a generalizability study and intra-class correlation coefficients. Results . Missing and inconsistent responses were < 2.6 %. The valuations were consistent across panels, with generalizability coefficients of 0.78 (VAS) and 0.64 (TTO). Within the main population panel, internal consistency was satisfactory and the influence of background characteristics negligible. Test-retest reliability was high, with generalizability coefficients of 0.90 (VAS) and 0.72 (TTO). Conclusion . Feasibility and reliability of the APM for realistic health profiles are good to excellent. The APM is a promising step to bridge the gap between the quality-adjusted life year methodology and clinical reality.

Tests of utility independence when health varies over time

In the conventional quality adjusted life year (QALY) model, people's preferences are assumed to satisfy utility independence. When health varies over time, utility independence implies that the value attached to a health state is independent of the health state that arise before or after it. Two separate studies were conducted involving a total of 155 respondents. In study one, we conducted five tests of utility independence using a standard gamble question. Three of the tests of utility independence were repeated in study two after randomisation was introduced in order to take account of possible ordering effects. Utility independence holds in the majority of cases examined here and so our work generally supports the use of utility independence to derive more tractable models.

What difference does it make? The calculation of QALY gains from health profiles using patient and general population values

OBJECTIVES

To compare the Quality-Adjusted Life Year (QALY) values produced from a direct health profile QALY calculation method, using patient values, with those derived from a conventional QALY calculation method, using general population values.

METHODS

Comparison of QALY values generated from patient valuations of health profiles, using a chained version of the Time Trade-Off method, with QALY values derived from a conventional QALY calculation method, using general population values of EQ-5D states, an observational survey of MS patients, and a randomized controlled trial.

RESULTS

Using patient valuations of health profiles, QALY values of treatment and placebo were 2.610 and 2.568, respectively, generating a gain of 0.042. The conventional QALY method gave values of 2.042 versus 1.998, producing a gain of 0.044. These findings were generally robust under sensitivity analyses.

CONCLUSIONS

QALY values were dependent on the calculation method used, but QALY gains were similar between methods. QALY values from the conventional QALY calculation method appeared robust to most changes in the assumptions used to derive values. The direct health profile QALY method was however more able to account for heterogeneity in preferences.

Estimating Preference Scores in Conventional and Home Nocturnal Hemodialysis Patients

Previous studies have reported higher quality of life in patients who receive home nocturnal hemodialysis (HNHD) than conventional in-center hemodialysis (IHD). The optimal method for eliciting preferences from dialysis patients remains undefined, and there may be unique methodologic concerns in this population. Patients' preferences for IHD (n = 20) and HNHD (n = 24) were studied using the standard gamble (SG), time trade-off (TTO), and modified willingness to pay (WTP) methods. This report describes experience with operationalizing these three techniques in this population. A higher preference for HNHD was found with all measures, with significant differences observed with the SG (HNHD: median 0.79 [interquartile range (IQR) 0.67 to 0.95]; IHD: median 0.60 [IQR 0.20 to 0.82]; P = 0.031) and WTP (HNHD: median 0.50 [IQR 0.40 to 0.68]; IHD: median 0.20 [IQR 0.20 to 0.38]; P < 0.001). SG and TTO scores were moderately correlated but not with WTP. In addition, qualitative issues arose during TTO and WTP interviews that seemed to influence the interpretation of these preference scores. In the TTO, time willing to trade became oriented toward the next pivotal life event, with a failure of the requirement for a constant proportional time trade-off. WTP preferences were oriented toward the smallest survival stipend. These issues represent range restriction biases. No significant issues arose during the SG interviews. HNHD patients expressed a greater preference for current health than IHD patients. The operational performance of SG was good in this study, whereas biases and methodologic concerns were identified with the TTO and WTP in this population.

Can differences in breast cancer utilities explain disparities in breast cancer care?

BACKGROUND

Black, older, and less affluent women are less likely to receive adjuvant breast cancer therapy than their counterparts. Whereas preference contributes to disparities in other health care scenarios, it is unclear if preference explains differential rates of breast cancer care.

OBJECTIVE

To ascertain utilities from women of diverse backgrounds for the different stages of, and treatments for, breast cancer and to determine whether a treatment decision modeled from utilities is associated with socio-demographic characteristics.

PARTICIPANTS

A stratified sample (by age and race) of 156 English-speaking women over 25 years old not currently undergoing breast cancer treatment.

DESIGN AND MEASUREMENTS

We assessed utilities using standard gamble for 5 breast cancer stages, and time-tradeoff for 3 therapeutic modalities. We incorporated each subject's utilities into a Markov model to determine whether her quality-adjusted life expectancy would be maximized with chemotherapy for a hypothetical, current diagnosis of stage II breast cancer. We used logistic regression to determine whether socio-demographic variables were associated with this optimal strategy.

RESULTS

Median utilities for the 8 health states were: stage I disease, 0.91 (interquartile range 0.50 to 1.00); stage II, 0.75 (0.26 to 0.99); stage III, 0.51 (0.25 to 0.94); stage IV (estrogen receptor positive), 0.36 (0 to 0.75); stage IV (estrogen receptor negative), 0.40 (0 to 0.79); chemotherapy 0.50 (0 to 0.92); hormonal therapy 0.58 (0 to 1); and radiation therapy 0.83 (0.10 to 1). Utilities for early stage disease and treatment modalities, but not metastatic disease, varied with socio-demographic characteristics. One hundred and twenty-two of 156 subjects had utilities that maximized quality-adjusted life expectancy given stage II breast cancer with chemotherapy. Age over 50, black race, and low household income were associated with at least 5-fold lower odds of maximizing quality-adjusted life expectancy with chemotherapy, whereas women who were married or had a significant other were 4-fold more likely to maximize quality-adjusted life expectancy with chemotherapy.

CONCLUSIONS

Differences in utility for breast cancer health states may partially explain the lower rate of adjuvant therapy for black, older, and less affluent women. Further work must clarify whether these differences result from health preference alone or reflect women's perceptions of sources of disparity, such as access to care, poor communication with providers, limitations in health knowledge or in obtaining social and workplace support during therapy.

Towards a better QALY model

This paper presents a test of the predictive validity of various classes of QALY models (i.e. linear, power and exponential models). We first estimated TTO utilities for 43 EQ-5D chronic health states and next these states were embedded in nonchronic health profiles. The chronic TTO utilities were then used to predict the responses to TTO questions with nonchronic health profiles. We find that the power QALY model clearly outperforms linear and exponential QALY models. Optimal power coefficient is 0.65. Our results suggest that TTO-based QALY calculations may be biased. This bias can be corrected using a power QALY model.

Exploring challenges to TTO utilities: valuing states worse than dead

The conventional time trade off (TTO) method relies on fundamentally different procedures to assess states better than and worse than dead. Arbitrary transformation mechanisms are then applied to worse than dead scores in order to achieve symmetry with those rated as better than dead. We use a 'life profile' approach along with a ranking procedure in order to show how states rated worse than dead may be assessed in exactly the same manner as better than dead scores. We then explore a common issue associated with states worse than dead that has received some attention recently: maximal endurable time. Our results showed that, although the severe health state was commonly rated as worse than dead, there were relatively few respondents that exhibited MET preferences. We discuss the implications of our findings for the use of the TTO method in deriving values for states that are worse than dead.

Time preference bias in time trade-off

This study examined whether time trade-off (TTO) values adjusted for time preferences are more consistent with individuals' preferences. This was carried out by testing the constant proportional trade-off (CPTO) assumption, and both individual specific and standard discount rates were used. The results show that the mean adjustment factor is around 0.03. This may influence relative cost-effectiveness in economic evaluations. The CPTO assumption holds with respect to both unadjusted TTO values and TTO values adjusted for individuals'time preference, and therefore no conclusions can be drawn as to whether the adjusted values are more consistent with individuals' preferences. However, the CPTO assumption is violated when standard discount rates are used. This clearly shows that the use of standard discount rates should be avoided. Further exploration of the time preference bias and other biases in TTO is identified as an important area of future research.

Quantifying trade-offs: quality of life and quality-adjusted survival in a randomised trial of chemotherapy in postmenopausal patients with lymph node-negative breast cancer

We evaluated quality of life (QL) and quality-adjusted survival in International Breast Cancer Study Group Trial IX, a randomised trial including 1669 eligible patients receiving tamoxifen for 5 years or three prior cycles of cyclophosphamide, methotrexate and 5-fluorouracil (CMF) followed by 57 months tamoxifen. During the time with CMF toxicity (Tox), without symptoms and toxicity (TWiST), and following relapse (Rel), patients scored their QL indicators and a utility indicator for subjective health estimation between ‘perfect’ and ‘worst’ health. Scores were averaged within Tox, TWiST and Rel and transformed to utilities. Mean durations for the three transition times were weighted with utilities to obtain mean quality-adjusted TWiST (Q-TWiST). Patients receiving CMF reported significantly worse scores for most QL domains at month 3, but less hot flushes. After completing chemotherapy, there were no differences by treatment groups. Benefits evaluated by Q-TWiST favoured the additional chemotherapy. CMF provided 3 more months of Q-TWiST for patients with ER-negative tumours, but CMF provided no benefit in Q-TWiST for patients with ER-positive tumours. Q-TWiST analysis based on patient ratings is feasible in large-scale cross-cultural clinical trials.