Effects on preferences of violations of procedural invariance.

BACKGROUND: In studies of health preferences, utilities for hypothetical health states cannot always be successfully measured. One marker for unsuccessful measurement is violation of "procedural invariance": when the ranking of two health states varies across assessment procedures. Using preference values based on unsuccessful measurement may result in misinterpretation of patients' attitudes about health. OBJECTIVE: The authors sought to determine whether people who violated procedural invariance had different preferences than people who satisfied it. METHODS: They performed secondary analyses of three completed studies that used the same two assessment procedures, identifying participants who violated procedural invariance and comparing the mean standard gamble (SG) and visual analog scale (VAS) scores of violators and satisfiers. PARTICIPANTS: Experiment 1, 30 healthy volunteers and 30 patients with cardiac arrhythmias; experiment 2, 139 patients with depressive illness; experiment 3, 98 family members of patients with schizophrenia. RESULTS: Rates of violation of procedural invariance ranged from 16% to 32%. Violation of procedural invariance was not associated with age, education level, race, or gender. Subjects with violations of procedural invariance had, in general, less ability to discriminate among states and less reliable VAS and SG measurements, and sometimes had different mean SG and VAS values. CONCLUSIONS: Violation of procedural invariance of preferences across scaling methods may be a signal for failure of the measurement process. Researchers should test for procedural invariance and consider reporting data separately for satisfiers and violators.     

A single European currency for EQ-5D health states

The EQ-5D questionnaire is a widely used generic instrument for describing and valuing health that was developed by the EuroQol Group. A primary objective of the EuroQol Group is the investigation of values for health states in the general population in different countries. As part of the EuroQol enterprise 11 population surveys were carried out in six Western European countries (Finland, Germany, The Netherlands, Spain, Sweden and the UK) to value health states as defined by the EQ-5D using a standardised visual analogue scale (EQ-5D VAS). This contribution reports how a European set of general population preference weights was derived from the data collected in the 11 valuation studies. The scores from this set of preference weights can be applied to generate a VAS-based weighted health status index for all the potential 243 EQ-5D health states for use in multi-national studies. To estimate the preference weights a multi-level regression analysis was performed on 82,910 valuations of 44 EQ-5D health states elicited from 6,870 respondents. Stable and plausible solutions were found for the model parameters. The R(2) value was 75%. The analysis showed that the major source of variance, apart from 'random error', was variance between individuals (28.3% of the total residual variance). These results suggest that VAS values for EQ-5D health states in six Western European countries can be described by a common model.     

The effect of individually assessed preference weights on the relationship between holistic utilities and nonpreference-based assessment

In the assessment of health-related quality of life, nonpreference-based methods usually show only moderate correlations with utility-based measures. One cause may be that patients assign different weights to the various domains of health-related quality of life, for which nonpreference-based methods usually do not allow. Utilities reflect a weighted sum of these domains. The aim of this study is to assess whether the relationship between utility-based methods and nonpreference-based measures improves through the use of individual importance weights for the various domains of health-related quality of life. For this purpose, weights were obtained from 41 early-stage breast cancer patients, both before and during treatment, for seven pre-selected health status attributes representing important domains of health-related quality of life during chemotherapy. The importance weights were combined with the level of functioning on the attributes. These scores were regressed against patients' utilities for their actually experienced health state during chemotherapy, measured by means of a visual analog scale (VAS), a time trade-off (TTO), and a standard gamble (SG). Before weighting, the seven attribute scores were more strongly related to TTO and SG utilities than the nonpreference-based questionnaires. However, when they were combined with the importance weights, only the correlation with the SG utilities improved, and only so with the importance weights obtained before chemotherapy. In this study, assigning individually assessed preference weights to self-reported level of functioning did not result in stronger relationships with utilities. This revised version was published online in June 2006 with corrections to the Cover Date.     

Health State Valuation Methods and Reference Points: The Case of Tinnitus

Objectives:  Many studies support the finding that patients, compared to the general public, valuate a given health condition differently. Based on Prospect Theory, this difference can be explained by adaptation processes resulting in differences in individual reference points. Using tinnitus as a case in point, our objective is to analyze empirically to what extent differences in risk attitudes (as a proxy to reference points) mediate differences in health valuations.
Methods:  Two hundred ten tinnitus patients and a similar number of unaffected persons indicated their willingness to undergo, hypothetically, an intervention (surgery or treatment) that would either improve or worsen the condition, thus revealing their risk attitudes. Utilities were elicited using three different methods: visual analogue scale (VAS), time trade-off (TTO), and standard gamble (SG). Repeated measure analysis of variance was used to test for mediation of utility differences by reference points.
Results:  Health status (affected–unaffected) has a significant effect on tinnitus utilities and risk attitude; at the same time, the latter is significantly associated with utilities. Adjusting for risk attitude, differences by health status disappear for SG and TTO, and are alleviated for VAS.
Conclusion:  Reference points in terms of risk attitudes are a potential confounder in the valuation of health states. Taking into account theoretical predictions and issues in measuring SG, TTO, and risk attitudes, these results cast doubt on the construct validity of SG and TTO, and point to the need to recognize and further clarify the role of reference points in health valuation research.     

Incorporating feelings related to the uncertainty about future health in utility measurement

The cost-effectiveness of health-care interventions is often evaluated using quality-adjusted life years (QALYs) as a measure of outcome. QALYs are valid representations of welfare only under the questionable assumption of additive independence of utility of health states across time periods. Therefore, some alternatives to QALYs have been proposed, among them healthy-year equivalents (HYEs) (Med. Decis. Making 1989; 9(2):142-149) and a semi-separable utility function (SSUF) (J. Health Econ. 2005; 24(1):33-54). This paper shows that HYEs using a single probability-equivalent standard gamble (SG) question measure the same health construct as the SSUF, which uses a series of probability-equivalent SG questions. The underlying assumption is that final health states are independent of initial health states. In contrast to the SSUF, however, HYEs are not bound by this assumption and also avoid propagating bias in the measurement of SG utilities from one question to the next. This paper also shows that both approaches can incorporate feelings related to the uncertainty about future health and capture them by using certainty equivalent questions.     

Can the standard gamble be used to determine utilities for uncertain health states? An example using postoperative maintenance therapy in Crohn's disease.

The objective of this study was to determine whether patients with Crohn's disease (CD) value the absolute reduction in postoperative recurrence risk attributable to therapy with mesalamine (5-ASA). One hundred subjects evaluated state A (taking 5-ASA; 25% risk of recurrence), state B (not taking 5-ASA; 40% risk of recurrence), and state C (100% risk of recurrence) by rank order, visual analog scale (VAS), and standard gamble (SG). Sixty-five of 91 patients (71%) with completed and usable questionnaires had the same preference order for state A (25% risk), state B (40% risk), and state C (100% risk) on both the VAS and the SG. The mean scores for state A (25% risk), state B (40% risk), and state C (100% risk), respectively, were 67.5, 49.8, and 19.8 on the VAS and 0.977, 0.972, and 0.910 on the SG. Subgroup analyses using stepwise logistic regression showed that risk attitude seemed to be predictive of subjects' preferences for 5-ASA. These results suggest that most subjects seem to value the 15% absolute risk reduction offered by 5-ASA. Furthermore, the SG seems to be a feasible method for measuring utilities for uncertain health states in patients with CD.     

Validity of utilities of patients with esophageal cancer

OBJECTIVES: The convergent validity between utility assessment methods was assessed. METHODS: Investigated were patients with esophageal cancer treated surgically with curative intent. Patients were interviewed in a period from 3 to 12 months after surgical resection. Patients evaluated their actual health and seven other states. Visual analogue scale (VAS) and standard gamble (SG) utilities were obtained for the health states in an interview. Patients also indicated whether or not they preferred death to living in a health state (worse than dead [WTD] preferences). RESULTS: Fifty patients completed the interview. Convergent validity was excellent at the aggregate and individual level. However, the relation between VAS and SG differed strongly across individuals. On a scale from 0 (dead) to 100 (perfect health), SG scores were lower for patients with WTD preferences (mean difference d = 35; p = .002); however, VAS scores did not vary by WTD preferences. CONCLUSIONS: In general, there is good agreement between VAS and SG measures, although patients disagree about how the VAS and SG are related. The standard gamble varied by WTD preferences, however, the VAS did not.     

Utilities derived from visual analog scale scores in patients with HIV/AIDS.

BACKGROUND: Visual analog scale (VAS) scores are used as global quality-of-life indicators and, unlike true utilities (which assess the desirability of health states v. an external metric), are often collected in HIV-related clinical trials. The purpose of this study was to derive and evaluate transformations relating aggregate VAS scores to utilities for current health in patients with HIV/AIDS. METHODS: HIV-specific transformations were developed using linear and nonlinear regression to attain models that best fit mean VAS and standard gamble (SG) utility values directly derived from 299 patients with HIV/AIDS participating in a multicenter study of health values. The authors evaluated the transformations using VAS and SG utility values derived directly from patients in other HIV/AIDS studies. Derived transformations were also compared with published transformations. RESULTS: A simple linear transformation was derived (u = 0.44v + 0.49), as was the exponent for a curvilinear model (u = 1 - [1 - v]1.6), where u = the sample mean utility and v the sample mean VAS score. The curvilinear transformation predicted values within 0.10 of the actual SG utility in 5 of 8 estimates and within 0.05 in 3 of 8 estimates (absolute error ranged from -0.01 to +0.21). The linear transformation performed somewhat better, predicting within 0.10 of the actual SG value in 6 of 8 cases and within 0.05 in 5 of 8 estimates (absolute error ranged from -0.05 to +0.13). An alternative linear model (u = v + 0.018) derived from the literature performed similarly to our linear model (7 of 8 predictions within 0.10, 1 of 8 estimates within 0.05, and absolute error ranging from -0.15 to +0.10), whereas an alternative published curvilinear model (u = 1 - [1 - v]2.3) performed the least well (2 of 8 estimates within 0.10 of the actual values and no estimates within 0.05). CONCLUSIONS: Predicted utilities are a reasonable alternative for use in HIV/AIDS decision analyses and cost-effectiveness analyses. Linear transformations performed better than curvilinear transformations in this context and can be used to convert aggregate VAS scores to aggregate SG values in large HIV/AIDS studies that collect VAS data but not utilities.     

Estimation of Utility Weights for Prostate-related Health States in Korea

ObjectivesVery limited previous research has investigated the utility weights of prostate-related diseases in the general population in Korea. The purpose of this study was to calculate the utility of prostate-related health states in the Korean general public using the standard gamble (SG) method.MethodsSeven health states for hypothetical prostate cancers, 1 for benign prostate hyperplasia, and 1 for erectile dysfunction were developed based on patient education material and previous publications. In total, 460 responses from the Korean general population were used to analyze the utility of prostate-related health states. Computer-assisted personal interviews were conducted, and utility values were measured using a visual analogue scale (VAS) and SG. Mean utility values were calculated for each prostate-related health state.ResultsThe mean utility values of prostate cancer derived from SG ranged from 0.281 (metastatic castration-refractory prostate cancer) to 0.779 (localized prostate cancer requiring prostatectomy). The utility value of benign prostate hyperplasia was 0.871, and that of erectile dysfunction was 0.812. The utility values obtained using the SG method in all conditions were higher than the values obtained by VAS. There were no significant demographic variables affecting utility values in multivariate analysis.ConclusionsOur findings might be useful for economic evaluation and utility calculation of screening and interventions for prostate-related conditions in the general population.     

Preference-based measurement of health-related quality of life (HRQL) in children with chronic musculoskeletal disorders (MSKDs).

BACKGROUND: Health-related quality of life can be measured by patients' health preferences (utilities or values). No method for measuring health state preferences has been standardized for children with arthritis or other musculoskeletal disorders (MSKDs). Such a method is needed for economic evaluations of current and new pediatric treatments. OBJECTIVES: 1) To assess the feasibility of utility measurements in children with MSKDs, 2) to test the validity of the Health Utility Index (HUI) for these children, 3) to assess whether rating scale values can be mathematically converted into meaningful standard gamble (SG) utilities, and 4) to study whether parents can act as proxies for their children with respect to health state preferences. METHODS: Eighty parents of children with MSKDs were consecutively sampled. Their children, if 8 years of age or older (n = 55), were studied concurrently. Utilities of current health states were obtained by using the SG and the HUI in random order. In addition, health state preferences were assessed using categorical and analog rating scales. Traditional nonutility measures of health status (the Childhood Health Assessment Questionnaire [CHAQ] and the Activities Scale for Kids [ASK]) were also completed. Intraclass correlation coefficients (ICCs) were calculated to assess concordance between the different utility measures and also between the ratings of the parents and their children. RESULTS: Children 8 years of age or older were able to express the strength of their health state preferences using the HUI and rating scales. Children older than 10 years of age were able to use the SG method. The health state utilities of the parents were higher than those of their children. The utilities varied widely depending on the elicitation method. The expected high agreement between the SG and the HUI was not found (ICC = 0.028 for parents, ICC = 0.016 for patients). Unlike the SG, the global utilities derived from the HUI agreed better with preferences derived from rating scales (ICC = 0.23-0.25) and correlated with traditional health status measures (with CHAQ, r = -0.56; with ASK, r = 0.46) both for parents and children. It was not possible to mathematically convert rating scale preferences into SG utilities. The SG utilities were unrelated to results from the rating scales, the CHAQ, and the ASK. Especially for parents, the SG utilities were very high, even when ratings of the other measures indicated poor health. CONCLUSIONS: Although it is possible to measure health utilities for children with MSKDs, the results are highly method dependent. The properties of the HUI in this population are more like those of the traditional health status measures rather than those of the SG. Preferences derived from rating scales, although easily performed, cannot readily be converted into SG utilities. Parents' ratings for their children are impaired by risk aversion.     

MHB4 Comparison of Standard Gamble, Time Trade-Off, and Visual Analog Scale Scores for Hypothetical Stroke Health States Using a Computer-Based Program

The most frequently used techniques for conducting utility assessments are the Standard Gamble (SG), the Time Trade-Off (TTO), and the Visual Analog Scale (VAS).
OBJECTIVES: The objectives of this study were to compare scores obtained on the SG, TTO, and VAS for hypothetical stroke health states; to determine the effect of age and gender on utility scores; to identify any ceiling or floor effects, and to determine the presence of interviewer effects.
METHODS: Forty-nine PharmD students from the College of Pharmacy at the University of Iowa were selected as the sample, and utility assessments were conducted by two interviewers, for hypothetical stroke scenarios adapted from the Glasgow Outcomes Sale. The health states evaluated were Good Recovery, Moderate Disability, Severe Disability, and a Vegetative State. Two rounds of interviews were separated by a period of 4 months. Regresion analysis was used to identify the factors influencing utility scores.
RESULTS: Mean SG scores for the four health states were 82.2, 62.7, 26.3, and 3.3, respectively. TTO scores for the four health states were 79.9, 57.3, 24.6, and 2.9, respectively. However, VAS scores were found to be higher than both TTO and SG scores. Neither age nor gender were found to be statistically significant determinants of reported utility scores. Interviewer effects were found for one out of 12 assessments in round 1, while none were observed in round 2. Floor effects were observed for all three techniques for the vegetative state.
CONCLUSION: Further research using larger, more representative samples from the general population is required to establish the validity of computer-based programs for utility assessments.     

A multi-method approach to measuring health-state valuations

Existing techniques for eliciting health-state valuations incorporate both strength of preferences for health states and other values such as risk aversion or time preference. This paper presents a new methodological approach that allows estimation of a set of core underlying health-state values based on responses elicited through multiple measurement techniques. A study was undertaken in which respondents completed the visual analogue (VAS) scale, time trade-off (TTO), standard gamble (SG) and person trade-off (PTO) for a range of states. By specifying flexible parametric functions to explain responses on each measurement technique, we estimated both the underlying strength of preference values for the health states in the study and the values for a set of auxiliary parameters characterising risk attitudes, discount rates, distributional concerns and scale distortion effects in the group of respondents. This study demonstrates that it is possible to understand responses on these four different measurement techniques based on a consistent set of core values. The approach presented here can provide insights into different sources of observed variation in VAS, TTO, SG and PTO responses and facilitate appropriate adjustment of valuations elicited through different methods for use in summary health measures and economic analyses.     

A comparison of standard gamble, time trade-off, and adjusted time trade-off scores

OBJECTIVE: To adjust patients' time trade-off (TTO) scores using information on their utility functions for survival time to derive a measure of health state utility equivalent to the standard gamble (SG). METHODS: A sample of 199 cardiovascular patients were asked three TTO and SG questions (to assess their own health state), and three certainty equivalent questions (to assess their utility function for survival time) in an interview. RESULTS: Patient's utility functions for time were increasingly concave, but being unable to model this successfully, a constant function with an averaged level of concavity was used. The raw TTO scores were significantly higher than SG scores, while the adjusted TTO scores were equivalent to the SG. CONCLUSIONS: Raw time trade-off scores will give biased estimates of health state utility when patients' utility functions for time are not linear, but these can be adjusted to yield true utilities. The constant proportional risk-posture assumption of the conventional QALY model, on which previous attempts to adjust time trade-offs have been based, was not supported by the data.     

Do Portuguese and UK health state values differ across valuation methods?

Purpose  

There has been an increasing interest in developing country-specific preference weights for widely used measures of health-related quality of life. The valuation of health states has usually been done using cardinal preference elicitation techniques of standard gamble (SG) or time trade-off (TTO). Yet there is increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to the more conventional cardinal techniques. This raises the issue of firstly whether ordinal and cardinal methods of preference elicitation provide similar results and secondly whether this relationship is robust across different valuation studies and different populations.     

Positive association between current health and health values for hypothetical disease states.

BACKGROUND: Valuations of hypothetical health state scenarios can be affected by participant characteristics. METHODS: The authors interviewed 108 veterans using the visual analogue scale (VAS), standard gamble (SG), time tradeoff (TTO), and willingness to pay (WTP) to measure health values for 1) current health and 2) 3 hypothetical health states portrayed in written scenarios describing cervical spondylotic myelopathy (CSM), a degenerative spine condition. They used bivariate rank order and multivariate regression analyses to assess the relationship between CSM values, participants' characteristics, and participants' current health values. RESULTS: Participants were predominantly male (89.8%) and Caucasian (75.9%), with a median age of 58.3 years and a median annual income of $15,000. Median values for current health were VAS, 0.75; SG, 0.80; TTO, 0.80; and WTP, $25,000. In the multivariate analysis, higher CSM values were associated with better current health as measured with the SG, TTO, and WTP (for all, P < 0.001); there was no association with VAS values (P = 0.157). CONCLUSIONS: Health values for CSM are positively associated with the current health of the study population.     

QALYs without bias? Nonparametric correction of time trade‐off and standard gamble weights based on prospect theory

Common health state valuation methodologies, such as standard gamble (SG) and time trade‐off (TTO), typically produce different weights for identical health states. We attempt to alleviate these differences by correcting the confounding influences modeled in prospect theory: loss aversion and probability weighting. Furthermore, we correct for nonlinear utility of life duration. In contrast to earlier attempts at correcting TTO and SG weights, we measure and correct all these tenets simultaneously, using newly developed nonparametric methodology. These corrections were applied to three less‐than‐perfect health states, measured with TTO and SG. We found considerable loss aversion and probability weighting for both gains and losses in life years, and we observe concave utility for gains and convex utility for losses in life years. After correction, the initially significant differences in weights between TTO and SG disappeared for all health states. Our findings suggest new opportunities to account for bias in health state valuations but also the need for further validation of resulting weights.