Impact of transformation of negative values and regression models on differences between the UK and US EQ-5D time trade-off value sets

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.

The EORTC QLU-C10D: The Canadian Valuation Study and Algorithm to Derive Cancer-Specific Utilities From the EORTC QLQ-C30

Objective. The EORTC QLQ-C30 is widely used for assessing quality of life in cancer. However, QLQ-C30 responses cannot be incorporated in cost-utility analysis because they are not based on general population's preferences, or utilities. To overcome this limitation, the QLU-C10D, a cancer-specific utility algorithm, was derived from the QLQ-C30. The aim of this study was to obtain Canadian population utility weights for the QLU-C10D. Methods. Respondents from a Canadian research panel expressed their preferences for 16 choice sets in an online discrete choice experiment. Each choice set consisted of two health states described by the 10 QLU-C10D domains plus an attribute representing duration of survival. Using a conditional logit model, responses were converted into utility decrements by evaluating the marginal rate of substitution between each QLU-C10D domain level with respect to duration. Results. A total of 3,363 individuals were recruited. A total of 2,345 completed at least one choice set and 2,271 completed all choice sets. The largest utility decrements were associated with the worse levels of Physical Functioning (-0.24), Pain (-0.18), Role Functioning (-0.15), Emotional Functioning (-0.12), and Nausea (-0.12). The remaining domains and levels had decrements of -0.05 to -0.09. The utility of the worst possible health state was -0.15. Conclusion. Respondents from the general population were most concerned with generic health domains, but Nausea and Bowel Problems also had an impact on the individual's utility. It is unclear as to whether cancer-specific domains will affect cost-utility analysis when evaluating cancer treatments; this will be tested in the next phase of the study.

Valuation of Health States Considered to Be Worse Than Death-An Analysis of Composite Time Trade-Off Data From 5 EQ-5D-5L Valuation Studies

OBJECTIVES

To evaluate the discriminative ability of negative values measured in 5-level EuroQol 5-dimensional questionnaire (EQ-5D-5L) value set studies.

METHODS

This is a secondary analysis of EQ-5D-5L value set studies from Singapore, the Netherlands, China, Thailand, and Canada in which health state values were elicited from a general population sample using a composite time trade-off (TTO) method. Mean values were calculated for health states with same severity. The association between the mean values and severity was evaluated using Pearson correlation (r). A linear mixed model using severity as the fixed effect was fitted for values. The analyses were performed separately for positive values (from a conventional TTO for health states considered "better than death") and negative values (from a lead time TTO for health states considered "worse than death").

RESULTS

In Singapore (N = 1000; negative values 32.6%), the mean decreased with severity from 0.89 to 0.21 for positive values and increased with severity from -0.98 to -0.89 for negative values. The correlation between values and severity was much lower for negative values (r = -0.016) than for positive values (r = -0.614). The coefficient of severity in the linear mixed model for negative values was much smaller (coefficient = -0.009; pseudo-R² < 0.001) compared with the model for positive values (coefficient = -0.041; pseudo-R² = 0.337). Results using data sets from the other countries were similar.

CONCLUSIONS

Negative values are not associated with severity of health states in EQ-5D-5L valuation studies, suggesting poor discriminative ability of the lead time TTO method in valuing health states considered worse than death.

Modelling the cost-effectiveness of PCSK9 inhibitors vs. ezetimibe through LDL-C reductions in a Norwegian setting

Aims

Despite the success of statins, there remains unmet clinical need in cardiovascular disease (CVD) prevention. New proprotein convertase subtilisin/kexin type 9 (PCSK9) inhibitors reduce low-density lipoprotein cholesterol (LDL-C) by 55-65%. Two PCSK9 inhibitors, evolocumab, and alirocumab, were approved for use in Norway but not yet for reimbursement through public national insurance. We aim to explore the cost-effectiveness of these compared with available treatments in a Norwegian setting.

Methods and results

A state transition Markov model was developed to model the cost-effectiveness of PCSK9 inhibitors for prevention of coronary heart disease, ischaemic strokes, and death among high-risk patient subpopulations in Norway, in both primary and secondary settings. Evolocumab and alirocumab are compared against ezetimibe and standard treatment. Risk of CVD is based on population incidence rates and adjusted according to baseline risk factors. Preventative effect of treatment was modelled according to absolute reduction in LDL-C. PCSK9 inhibitors were never found to be cost-effective in primary prevention. In secondary prevention they were cost-effective only for older, high-risk patients. The lowest cost-effectiveness ratios were for heterozygous familial hypercholesterolaemia patients and high-risk diabetics, with €63 200 and €68 400 per quality-adjusted life-year, respectively.

Conclusion

High lifetime costs of PCSK9 inhibitors may not be offset by estimated health gains for most eligible patients. PCSK9 inhibitors are found in the model only to be cost-effective in secondary prevention for older patients with high absolute risk of CVD. This picture is likely to change as price decreases. Future research is needed to determine the long-term preventative effects of PCSK9 inhibitors.

International comparison of experience-based health state values at the population level

BACKGROUND

Decision makers need to know whether health state values, an important component of summary measures of health, are valid for their target population. A key outcome is the individuals' valuation of their current health. This experience-based perspective is increasingly used to derive health state values. This study is the first to compare such experience-based valuations at the population level across countries.

METHODS

We examined the relationship between respondents' self-rated health as measured by the EQ-VAS, and the different dimensions and levels of the EQ-5D-3 L. The dataset included almost 32,000 survey respondents from 15 countries. We estimated generalized linear models with logit link function, including country-specific models and pooled-data models with country effects.

RESULTS

The results showed significant and meaningful differences in the valuation of health states and individual health dimensions between countries, even though similarities were present too. Between countries, coefficients correlated positively for the values of mobility, self-care and usual activities, but not for the values of pain and anxiety, thus underlining structural differences.

CONCLUSIONS

The findings indicate that, ideally, population-specific experience-based value sets are developed and used for the calculation of health outcomes. Otherwise, sensitivity analyses are needed. Furthermore, transferring the results of foreign studies into the national context should be performed with caution. We recommend future studies to investigate the causes of differences in experience-based health state values through a single international study possibly complemented with qualitative research on the determinants of valuation.

EuroQol Protocols for Time Trade-Off Valuation of Health Outcomes

The time trade-off (TTO) valuation technique is widely used to determine utility values of health outcomes to inform quality-adjusted life-year (QALY) calculations for use in economic evaluation. Protocols for implementing TTO vary in aspects such as the trade-off framework, iteration procedure and its administration model and method, training of respondents and interviewers, and quality control of data collection. The most widely studied and utilized TTO valuation protocols are the Measurement and Valuation of Health (MVH) protocol, the Paris protocol and the EuroQol Valuation Technology (EQ-VT) protocol, all developed by members of the EuroQol Group. The MVH protocol and its successor, the Paris protocol, were developed for valuation of EQ-5D-3L health states. Both protocols were designed for a trained interviewer to elicit preferences from a respondent using the conventional TTO framework with a fixed time horizon of 10 years and an iteration procedure combining bisection and titration. Developed for valuation of EQ-5D-5L health states, the EQ-VT protocol adopted a composite TTO framework and made use of computer technology to facilitate data collection. Training and monitoring of interviewers and respondents is a pivotal component of the EQ-VT protocol. Research is underway aiming to further improve the EuroQol protocols, which form an important basis for the current practice of health technology assessment in many countries.

Adjustment of foreign EQ-5D-3L utilities can increase their transferability

Background

Foreign utilities of the EQ-5D-3L (3-level version of the EuroQol-5 Dimension of health questionnaire) are not readily transferrable to economic evaluations conducted from a national perspective. It has been advised to avoid transferring mean utilities from one country to another without adjusting them; yet no such method exists.

Purpose

The present study aimed to develop a method for adjusting mean utilities to increase their transferability from one country to another.

Methods

Seven datasets containing EQ-5D-3L answers were valued using value sets from four countries: the UK, the Netherlands, Germany, and Spain. Hereby, seven mean utility values were obtained for each country. This allowed for three pairwise comparisons: 1) UK mean values vs Dutch mean values; 2) UK mean values vs German mean values; and 3) UK mean values vs Spanish mean values. For each of these three comparisons, a regression model was fitted using the mean UK utilities as the dependent variable and the other country’s mean utilities as the independent variable. The coefficients from the three regression models were validated using results from a published article containing mean utilities obtained by valuing the EQ-5D-3L data using all four value sets.

Results

The findings suggested that adjustment of foreign utilities may increase transferability between countries where value sets are not comparable. It was possible to adjust the mean utilities valued by the Dutch and German value sets to make them reflect mean UK utilities as there were substantial differences between these value sets. Transferability of the Spanish mean utility values was not improved as the Spanish and UK value sets are sufficiently similar.

Conclusion

It is feasible to adjust foreign mean utilities of the EQ-5D-3L to make them reflect national preferences for health.

Italian population-based values of EQ-5D health states

OBJECTIVE

To estimate a value set for the calculation of Italian-specific quality-adjusted life years (QALYs), based on preferences elicited on EuroQol five-dimensional (EQ-5D) questionnaire health states using the time trade-off technique.

METHODS

The revised standard Measurement and Valuation of Health protocol was followed. Twenty-five health states, divided into three groups and given to 450 subjects, were selected to obtain 300 observations per state. Subjects aged 18 to 75 years were recruited to be representative of the Italian general adult population for age, sex, and geographical distribution. To improve efficiency, face-to-face interviews were conducted by using the Computer Assisted Personal Interviewing approach. Several random effects regression models were tested to predict the full set of EQ-5D questionnaire health states. Model selection was based on logical consistency of the estimates, sign and magnitude of the regression coefficients, goodness of fit, and parsimony.

RESULTS

The model that satisfied the criteria of logical consistency and was more efficient includes 10 main effect dummy variables for the EQ-5D questionnaire domain levels and the D1 interaction term, which accounts for the number of dimensions at levels 2 or 3 beyond the first. This model has an R(2) of 0.389 and a mean absolute error of 0.03, which are comparable to or better than those of models used in other countries. The utility estimates after state 11111 range from 0.92 (21111) to -0.38 (33333). Italian utility estimates are higher than those estimated in the United Kingdom and Spain and used so far to assess QALYs and conduct cost-utility evaluations in Italy.

CONCLUSIONS

A specific value set is now available to calculate QALYs for the conduction of health economic studies targeted at the Italian health care system.

Time trade-off and attitudes toward euthanasia: implications of using 'death' as an anchor in health state valuation

PURPOSE

Health state values are by convention anchored to 'perfect health' and 'death.' Attitudes toward death may consequently influence the valuations. We used attitudes toward euthanasia (ATE) as a sub-construct for attitudes toward death. We compared the influence on values elicited with time trade-off (TTO), lead-time TTO (LT-TTO) and visual analogue scale (VAS).Since the 'death' anchor is most explicit in TTO, we hypothesized that TTO values would be most influenced by ATE.

METHODS

Respondents valued eight EQ-5D health states with VAS, then TTO (n = 328) or LT-TTO (n = 484). We measured ATE on a scale from -2 (fully disagree) to 2 (fully agree) and used multiple linear regressions to predict VAS, TTO, and LT-TTO values by ATE, sex, age, and education.

RESULTS

A one-point increase on the ATE scale predicted a mean TTO value change of -.113 and LT-TTO change of -.072. Demographic variables, but not ATE, predicted VAS values.

CONCLUSIONS

TTO appears to measure ATE in addition to preferences for health states. Different ways of incorporating death in the valuation may impact substantially on the resulting values. 'Death' is a metaphysically unknown concept, and implications of attitudes toward death should be investigated further to evaluate the appropriateness of using 'death' as an anchor.