The transformation of utilities for health states worse than death: consequences for the estimation of EQ-5D value sets.
ABSTRACT Utilities for health are measured on an interval scale, where 1 refers to full health and 0 refers to death. No theoretical lower boundary on the utilities for states worse than death exists. As a consequence, negative values receive greater weight in the calculation of mean utilities. To avoid this, negative values often are bound at -1.
The objective of this study was to compare the effect of 3 methods to bound negative values at -1 on the estimation of EQ-5D value sets: truncation, monotonic, and linear transformation.
Data of the Dutch EQ-5D valuation study were used. A total of 298 respondents directly valued 17 EQ-5D health states using the time trade-off (TTO) method. Random effects regression analysis was used to interpolate TTO values for all possible EQ-5D states. In the regression analysis the dependent variable is 1 minus the TTO value and the independent variables describe the health state. Two widely used models to estimate EQ-5D value were applied after truncation of negative values and monotonic and linear transformation of negative values. Both models also were estimated on medians.
Truncation of negative values gave the largest mean absolute error (MAE); the linear transformation resulted in the smallest MAE. When medians were used for estimation, the MAEs were comparable with the estimation on means.
The choice of a method to bound negative values is arbitrary and affects the resulting value set. For the estimation of EQ-5D value sets from a societal perspective the use of medians should be considered.
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ABSTRACT: 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. 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. 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. An agency for market research recruited 212 Dutch respondents aged 18-75 years. 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. For many subjective health outcomes, Thurstone scaling and its derivatives may be an attractive methodology to arrive at quantitative measures.Medical Care 05/2008; 46(4):357-65. · 3.41 Impact Factor
Article: Canadian valuation of EQ-5D health states: preliminary value set and considerations for future valuation studies.[show abstract] [hide abstract]
ABSTRACT: The EQ-5D is a preference based instrument which provides a description of a respondent's health status, and an empirically derived value for that health state often from a representative sample of the general population. It is commonly used to derive Quality Adjusted Life Year calculations (QALY) in economic evaluations. However, values for health states have been found to differ between countries. The objective of this study was to develop a set of values for the EQ-5D health states for use in Canada. Values for 48 different EQ-5D health states were elicited using the Time Trade Off (TTO) via a web survey in English. A random effect model was fitted to the data to estimate values for all 243 health states of the EQ-5D. Various model specifications were explored. Comparisons with EQ-5D values from the UK and US were made. Sensitivity analysis explored different transformations of values worse than dead, and exclusion criteria of subjects. The final model was estimated from the values of 1145 subjects with socio-demographics broadly representative of Canadian general population with the exception of Quebec. This yielded a good fit with observed TTO values, with an overall R2 of 0.403 and a mean absolute error of 0.044. A preference-weight algorithm for Canadian studies that include the EQ-5D is developed. The primary limitations regarded the representativeness of the final sample, given the language used (English only), the method of recruitment, and the difficulty in the task. Insights into potential issues for conducting valuation studies in countries as large and diverse as Canada are gained.PLoS ONE 01/2012; 7(2):e31115. · 4.09 Impact Factor
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ABSTRACT: To elicit neck pain (NP) patients' preference scores for their current health, and investigate the association between their scores and NP disability. Rating scale scores (RSs) and standard gamble scores (SGs) for current health were elicited from chronic NP patients (n=104) and patients with NP following a motor vehicle accident (n=116). Patients were stratified into Von Korff Pain Grades: Grade I (low-intensity pain, few activity limitations); Grade II (high-intensity pain, few activity limitations); Grade III (pain with high disability levels, moderate activity limitations); and Grade IV (pain with high disability levels, several activity limitations). Multivariable regression quantified the association between preference scores and NP disability. Mean SGs and RSs were as follows: Grade I patients: 0.81, 0.76; Grade II: 0.70, 0.60; Grade III: 0.64, 0.44; Grade IV: 0.57, 0.39. The association between preference scores and NP disability depended on type of NP and preference-elicitation method. Chronic NP patients' scores were more strongly associated with depressive symptoms than with NP disability. In both samples, NP disability explained little more than random variance in SGs, and up to 51% of variance in RSs. Health-related quality-of-life is considerably diminished in NP patients. Depressive symptoms and preference-elicitation methods influence preference scores that NP patients assign to their health.Quality of Life Research 03/2010; 19(5):687-700. · 2.30 Impact Factor