Standard Gamble Utilities Research Articles

A Consistency Test of the Time Trade-Off

This paper tests the internal consistency of time trade-off utilities. We find significant violations of consistency in the direction predicted by loss aversion. The violations disappear for higher gauge durations. We show that loss aversion can also explain that for short gauge durations time trade-off utilities exceed standard gamble utilities. Our results suggest that time trade-off measurements that use relatively short gauge durations, like the widely used EuroQol algorithm (Dolan 1997), are affected by loss aversion and lead to utilities that are too high.

Disease progression in amyotrophic lateral sclerosis

This study reports the results of a long-term economic evaluation of riluzole in the treatment of amyotrophic lateral sclerosis (ALS) versus best supportive care in the United Kingdom. The analysis included in this contribution aims to provide an update of the determination of the phase of the disease that is prolonged by riluzole and also to assess the quality of the life extension offered by riluzole by taking into account the patients' utility score. Specifically, the analysis provides a more specific estimate of the cost-utility of riluzole dependent disease stage, thereby providing a useful insight of the cost-effectiveness of therapy. A Markov model was used to assess the cost-effectiveness of riluzole versus best supportive care. Transition possibilities and the distribution of patients by health states were taken from a cohort of 954 patients drawn from a large randomised, double blind, placebo-controlled, multicentre trial between 1992 and 1994. Costs associated with riluzole included the acquisition cost and bi-monthly monitoring for raised ALT levels. Patient assessed utilities were collected by use of the SG technique from two centres (King's, London and Preston) in the UK. Four distinct health states were used corresponding to mild, moderate, severe and terminal states. Applying the Markov model and extending the transitional probabilities using linear interpolation, the base case cost per life year gained was estimated at 15,192 pounds while applying Standard Gamble utility scores, the base case cost per quality-adjusted life-year (QALY) was assessed at 22,086 pounds. Carrying out a probabilistic sensitivity analysis, the cost per QALY was estimated at 22,236 pounds with standard deviation of 612 pounds. The results of the long-term analysis also show that riluzole on average increases survival in ALS patients by 6 months with approximately 5 months of the additional life gained in the early disease states, of which 4 months is spent in disease state 2, where quality of life is relatively high. However, the model is sensitive in the way in which the long-term transitional probabilities are estimated. Using averages of the first nine cycles, the cost per QALY would increase to 33,420 pounds with standard deviation of 972 pounds. Thus, this analysis highlights some of the difficulties associated with extending the short clinical effectiveness data; one way forward would be to obtain long-term observations data for both groups.

Patient Preferences for Outcomes Associated With Surgical Management of Prostate Cancer

We used utility assessment to evaluate patient preferences for current urinary and sexual function after radical prostatectomy. We measured preferences in 209 community volunteers enrolled in a prostate cancer screening study who underwent radical prostatectomy between 1994 and 1998. We compared preferences in 3 outcome groups, namely men bothered by current urinary and sexual functioning, only bothered by current sexual functioning and not bothered by current sexual or urinary functioning. Preferences were assessed via a computer based interview using time trade-off and standard gamble methods. Current functioning was assessed via a standardized questionnaire. Median time trade-off and standard gamble utilities were high at 0.9 across outcome groups, indicating that men were not willing to give up many remaining life years (10% of remaining life expectancy) with current functioning to achieve ideal functioning. However, mean time trade-off and standard gamble scores significantly decreased as the burden increased in men bothered by current sexual and urinary function (0.77 and 0.82), bothered by current sexual function only (0.87 and 0.89) and not bothered by sexual or urinary function (0.92 and 0.96, respectively). Health related quality of life was generally good in this observational study of patients treated for prostate cancer with radical prostatectomy. In addition, those bothered by urinary and/or sexual function would not be willing to trade much of the remaining life span to achieve perfect functioning. However, the perception of side effects was bothersome enough in some men to warrant appropriate patient counseling regarding the potential risks and benefits.

A new explanation for the difference between time trade-off utilities and standard gamble utilities.

This paper gives a new explanation for the systematic disparity between standard gamble (SG) utilities and time trade-off (TTO) utilities. The common explanation, which is based on expected utility, is that the disparity is caused by curvature of the utility function for duration. This explanation is, however, incomplete. People violate expected utility and these violations lead to biases in SG and TTO utilities. The paper analyzes the impact on SG and TTO utilities of three main reasons why people violate expected utility: probability weighting, loss aversion, and scale compatibility. In the SG, the combined effect of utility curvature, probability weighting, loss aversion, and scale compatibility is an upward bias. In the TTO these factors lead both to upward and to downward biases. This analysis can also explain the tentative empirical finding that the TTO better describes people's preferences for health than the SG.

Multiattribute and single-attribute utility functions for the health utilities index mark 3 system.

The Health Utilities Index Mark 3 (HUI3) is a generic multiattribute preference-based measure of health status and health-related quality of life that is widely used as an outcome measure in clinical studies, in population health surveys, in the estimation of quality-adjusted life years, and in economic evaluations. HUI3 consists of eight attributes (or dimensions) of health status: vision, hearing, speech, ambulation, dexterity, emotion, cognition, and pain with 5 or 6 levels per attribute, varying from highly impaired to normal. The objectives are to present a multiattribute utility function and eight single-attribute utility functions for the HUI3 system based on community preferences. Two preference surveys were conducted. One, the modeling survey, collected preference scores for the estimation of the utility functions. The other, the direct survey, provided independent scores to assess the predictive validity of the utility functions. Preference measures included value scores obtained on the Feeling Thermometer and standard gamble utility scores obtained using the Chance Board. A random sample of the general population (> or =16 years of age) in Hamilton, Ontario, Canada. Estimates were obtained for eight single-attribute utility functions and an overall multiattribute utility function. The intraclass correlation coefficient between directly measured utility scores and scores generated by the multiattribute function for 73 health states was 0.88. The HUI3 scoring function has strong theoretical and empirical foundations. It performs well in predicting directly measured scores. The HUI3 system provides a practical way to obtain utility scores based on community preferences.

Assessing values for health: numeracy matters.

Patients' values are fundamental to decision models, cost-effectiveness analyses, and pharmacoeconomic analyses. The standard methods used to assess how patients value different health states are inherently quantitative. People without strong quantitative skills (i.e., low numeracy) may not be able to complete these tasks in a meaningful way. To determine whether the validity of utility assessments depends on the respondent's level of numeracy, the authors conducted in-person interviews and written surveys and assessed utility for the current health for 96 women volunteers. Numeracy was measured using a previously validated 3-item scale. The authors examined the correlation between self-reported health and utility for current health (assessed using the standard gamble, time trade-off, and visual analog techniques) across levels of numeracy. For half of the women, the authors also assessed standard gamble utility for 3 imagined health states (breast cancer, heart disease, and osteoporosis) and asked how much the women feared each disease. Respondent ages ranged from 50 to 79 years (mean = 63), all were high school graduates, and 52% had a college or postgraduate degree. Twenty-six percent answered 0 or only 1 of the numeracy questions correctly, 37% answered 2 correctly, and 37% answered all 3 correctly. Among women with the lowest level of numeracy, the correlation between utility for current health and self-reported health was in the wrong direction (i.e., worse health valued higher than better health): for standard gamble, Spearman r=-0.16, P = 0.44;for time trade-off, Spearman r=-0.13, P=0.54. Among the most numerate women, the authors observed a fair to moderate positive correlation with both standard gamble (Spearman r=0.22, P=0.19) and time trade-off (Spearman r=0.50, P=0.002). In contrast, using the visual analog scale, the authors observed a substantial correlation in the expected direction at all levels of numeracy (Spearman r= 0.82, 0.50, and 0.60 for women answering 0-1, 2, and 3 numeracy questions, respectively; all Ps < or = 0.003). With regard to the imagined health states, the most feared disease had the lowest utility for 35% of the women with the lowest numeracy compared to 76% of the women with the highest numeracy (P=0.03). The validity of standard utility assessments is related to the subject's facility with numbers. Limited numeracy may be an important barrier to meaningfully assessing patients' values using the standard gamble and time trade-off techniques.

The cost utility analysis of riluzole for the treatment of amyotrophic lateral sclerosis in the UK

This study reports the results of a long-term economic evaluation of riluzole in the treatment of amyotrophic lateral sclerosis (ALS) versus best supportive care in the United Kingdom. The aim was to assess the cost implications of the life extension offered by riluzole through cost utility analysis based on patient assessed utilities of different health states. A Markov model was used to assess the cost–effectiveness of Rilutek with best supportive care. Transition possibilities and the distribution of patients by health states were taken from a cohort of 954 patients drawn from a large randomised, double blind, placebo–controlled, multicentre trial between 1992 and 1994 in the first 18 months and used to extrapolate the model to assess the long-term prolongation of life. Four distinct health states were used corresponding to mild, moderate, severe and terminal states. Costs associated with Rilutek included the acquisition cost and bi-monthly monitoring for raised ALT levels. Patient assessed utilities were collected by use of the standard gamble technique. 77 patients were entered into the study from two centres (King's, London and Preston) in the UK. Mean utilities for each of the health states was generated and, given that the data were skewed, a sensitivity analysis was undertaken with the median utility values. The implications of life extension offered by riluzole versus best supportive care were assessed both in terms of life extension projected and quality adjusted survival using patient based utilities. Using the Markov model and the transitional probabilities the base case cost per life year gained was estimated at £14,370 and applying Standard Gamble utility scores, the base case cost per QALY was assessed as £20,904. The effect of discounting costs and benefits altered the cost effectiveness analysis to £17,760 per life year gained while a sensitivity analysis around median or mean scores for the utility weight resulted in a range of £19,020 to £25,794 per QALY gained.

A psychometric analysis of the measurement level of the rating scale, time trade-off, and standard gamble

A fundamental assumption of utility-based analyses is that patient utilities for health states can be measured on an equal-interval scale. This assumption, however, has not been widely examined. The objective of this study was to assess whether the rating scale (RS), standard gamble (SG), and time trade-off (TTO) utility elicitation methods function as equal-interval level scales. We wrote descriptions of eight prostate-cancer-related health states. In interviews with patients who had newly diagnosed, advanced prostate cancer, utilities for the health states were elicited using the RS, SG, and TTO methods. At the time of the study, 77 initial and 73 follow-up interviews had been conducted with a consecutive sample of 77 participants. Using a Rasch model, the boundaries (Thurstone Thresholds) between four equal score sub-ranges of the raw utilities were mapped onto an equal-interval logit scale. The distance between adjacent thresholds in logit units was calculated to determine whether the raw utilities were equal-interval. None of the utility scales functioned as interval-level scales in our sample. Therefore, since interval-level estimates are assumed in utility-based analyses, doubt is raised regarding the validity of findings from previous analyses based on these scales. Our findings need to be replicated in other contexts, and the practical impact of non-interval measurement on utility-based analyses should be explored. If cost-effectiveness analyses are not found to be robust to violations of the assumption that utilities are interval, serious doubt will be cast upon findings from utility-based analyses and upon the wisdom of expending millions in research dollars on utility-based studies.

CN2: EFFECT OF INCLUDING (VERSUS EXCLUDING) FATES WORSE THAN DEATH ON UTILITY MEASUREMENT

OBJECTIVE: To test impact of including (versus excluding) health states perceived to be worse than death on utility measurement using standard gamble (SG) and visual analogue scale (VAS) methods. METHODS: Face-to-face interviews were conducted in a convenience sample of women aged 22 to 50 years with no history of breast cancer or cancer requiring chemotherapy (n = 119). Data were collected between March 2000 and June 2000 at a Midwestern University in the US. Subjects were asked to rate their utility if faced with three hypothetical breast cancer health states: cure, treatment and recurrence. Utility weights were estimated using SG top-down titration and VAS methods scaled from zero (death) to one (perfect health). Linear transformation was used to allow for negative preference weights for health states worse than death. RESULTS: Unpaired t-test analysis showed statistically significant greater change in SG (n = 16) and VAS (n = 17) utilities for respondents perceiving cancer recurrence as worse than death than those perceiving death as least desirable health state (p < 0.05). Mean change in SG (VAS) utility allowing for health states worse than death for breast cancer cure versus treatment, treatment versus recurrence, and cure versus recurrence were 0.066(0.226), 0.335(0.339), and 0.401(0.564), respectively (n = 119). Excluding negative utilities from study resulted in statistically significant lower mean changes in utility weights (SG n = 103, VAS n = 102). CONCLUSION: Most studies typically measure health preferences excluding health states perceived as worse than death. Similar to Patrick et al (1994) results of this study indicate health preference elicitation methods can be successfully adapted to acquire negative utilities. Regardless of metric used, both SG and VAS yield higher changes in weight estimates when negative utilities are permitted. Addressing negative utilities in studies could significantly affect QALY estimates in economic analyses.

Preferences for quality of life or survival expressed by patients with heart failure

Background: As many patients with heart failure develop symptoms limiting daily life, newer therapies may be found to improve functional status without concomitant survival benefit. As some of these therapies may actually increase mortality, it is increasingly relevant to assess patients’ preferences for survival vs improvement in symptoms. Methods: We enrolled 99 patients with advanced heart failure (ejection fraction 24 ± 10, duration 6 ± 5 years). Each patient completed time trade-off and standard gamble instruments, Minnesota Living with Heart Failure questionnaires and visual analog scales for dyspnea and overall health. Jugular venous pressure was assessed in all patients and peak oxygen consumption was measured during bicycle exercise in 60 patients. Results: Strong polarity of preference toward either survival or quality of life was expressed by 60% of patients. There was good correlation between time trade-off and standard gamble utility scores ( r = 0.64), and between preference and functional class ( r = 0.60). Higher jugular venous pressure and lower peak oxygen consumption were associated with poorer utility scores ( p < .05). Higher dyspnea scores and worse Living with Heart Failure scores were also associated with preference to trade time or take risks for better health. Conclusions: These findings suggest that heart failure patients express meaningful preferences about quality vs length of life. High jugular venous pressure, low peak oxygen consumption and poor Living with Heart Failure scores were related to low utility scores. These cannot be assumed, however, to predict the intensity of individual preference to trade nothing or virtually everything for better health.

Lack of congruence in the ratings of patients' health status by patients and their physicians.

The purpose of this study was to examine if physician assessments of their patients' health status after the medical encounter are comparable to their patients' self-assessment of their own health. Consecutive patients with musculoskeletal diseases were recruited when they attended 1 of the rheumatology outpatient clinics selected for the study. Five physicians participated in the study, 4 based at an academic center and 1 in the community. Patients were interviewed after seeing the physician; they completed health status questionnaires (mHAQ and SF-12) and rated their pain, worry about disease, and overall health status on visual analog scales. Standard gamble techniques were used to obtain patient utilities in relation to their health status, "gambling" on the probability of obtaining perfect health from an intervention with varying risks of death. After the medical encounter, physicians were asked to rate their patients' health status with similar instruments and with standard gamble elicitation techniques, blinded to the patients' responses. A total of 105 patients participated in the study; 70% were female; mean age was 54+/-16 years; 64% had a connective tissue disease, most commonly rheumatoid arthritis; and the other diseases in this group included soft tissue rheumatism, osteoarthritis, or low back pain. Statistically significant differences were observed between patient and physician ratings for pain, overall health, and standard gamble. On average, physicians rated their patients' health status higher than the patients themselves and were less willing to gamble on the risk of death versus perfect health. Intraclass correlation coefficients (ICC) were low: 0.42 for pain, 0.11 for worry, 0.11 for overall health, and 0.04 for standard gamble utilities. Similar findings were observed when subgroup analysis was performed for individual physicians and for patients with connective tissue diseases. No specific patient characteristic consistently related to increased divergence in the ratings. These findings suggest that the communication between physicians and their patients at the time of the medical encounter needs to be enhanced. An understanding of their patients' health perceptions may assist physicians in suggesting appropriate interventions, taking into account their patients' benefit-risk preferences.

Visual analog scales, standard gambles, and relative risk aversion.

It has been argued that visual analog scales (VASs) elicit an individual's measurable value function. The theoretical link between an individual's measurable value function v(.) and his or her von Neumann-Morgenstem utility function u(.) appears to provide a justification for transforming VAS scores into standard gamble (SG) utilities. However, VAS scores have been found to be subject to the effects of context, which casts doubt that the procedure is properly revealing v(.). The authors tested for the effects of context on VAS and SG scores. They also explored whether the range-frequency (R-F) model of Parducci offers a means of correcting VAS scores for the effects of context. The R-F model may provide a means of correcting VAS scores for the effects of context, but no stable relationship exists between these corrected scores and SG utilities. Hence, there remain no grounds for transforming VAS scores into SG utilities.

Parental perspectives of the health status and health-related quality of life of teen-aged children who were extremely low birth weight and term controls.

To compare the health status and health-related quality of life of teen-aged children who were extremely low birth weight (ELBW) with matched controls from the perspective of their parents. Geographically defined cohort; longitudinal follow-up; cross-sectional interviews. parents of 149/169 (88%) ELBW children between 12 and 16 years of age (including 41 children with neurosensory impairments) and 126/145 (87%) parents of term controls. Health status of the teenagers was classified according to the 6 attributes of the Health Utilities Index Mark 2, based on information obtained during parent interviews. Parents were asked to imagine themselves living in their own child's health state and 4 preselected hypothetical health states when providing directly measured standard gamble utility scores. Parents of ELBW children reported a higher frequency and more complex functional limitations than parents of controls for their own children's health status. Also, the mean utilities were lower (ELBW =.91 vs controls =. 97) and the variability in their scores was greater. There were no differences in the valuation of the hypothetical health states provided by parents of ELBW and control children. ELBW children were reported to have a greater burden of disability than were control children based on parental descriptions. Nonetheless, parents of ELBW children, on average, rated the health-related quality of life of their children fairly high. Thus, differences in reported functional status are not necessarily associated with lower utility scores.

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.

The reliability and internal consistency of an Internet-capable computer program for measuring utilities.

The purpose of this study was to assess the reliability and internal consistency of measurements of utilities performed with a computer program (iMPACT2) designed for Internet surveys and Internet patient decision-support systems. We implemented the Internet Multimedia Preference Assessor Construction Tool, version 2 (iMPACT2) program using the combination of a web server, HTML files, and a web-accessible database. The program randomized subjects, screened their responses for missing data and failures of internal consistency, assisted patients with resolving certain inconsistencies, and, upon a subject's completion of the protocol, provided a report of results to the research assistant administering the program. To validate the iMPACT2 program, we recruited 60 healthy community volunteers and elicited preferences in a research-lab setting using a visual analog scale (VAS) and the standard gamble (SG) for subject's current health and three hypothetical states. For purposes of comparison, we also administered a Short Form-12 (SF-12) health-assessment questionnaire. Subjects used the computer software on two occasions separated by 2-4 weeks of time. Visual analog scale and standard gamble ratings for subjects' current health were reliable (intraclass correlation coefficient (ICC) of 0.82 and 0.84 (two outliers excluded -0.60 without exclusions), respectively) were comparable with the reliability of the Physical and Mental Component scales of the SF-12 (ICCs of 0.84 and 0.75, respectively). Subjects could easily discriminate between hypothetical states (D scores 0.74 for SG and 0.90 for VAS), and 94% had a completely internally consistent ordering of preference ratings for states. iMPACT2 produces measurements of standard gamble utilities that are reliable and have a high degree of internal consistency. Procedures for assessment of utilities developed for desktop computer programs can be translated to software designed for the Internet, facilitating the use of utilities and endpoints in clinical trials and development of web-based decision-support applications for patients. However, further testing, including direct comparisons with traditional interviewer administered utility elicitation protocols, is needed.

Patient utilities in chronic musculoskeletal pain: how useful is the standard gamble method?

The main goal of current pain management approaches is to increase the patients' quality of life by improving pain coping skills and by reducing the levels of disability in daily life, often despite persistent pain. Direct measurement of quality of life is of crucial importance in economic evaluation research, in which not only is the estimation of financial costs and benefits included, but so is the evaluation of costs and benefits in terms of changes in health states. The purpose of this study is to compare the psychometric qualities of two instruments for assessing patients' utilities, the rating scale (RS) and the standard gamble (SG). Such instruments are designed for their application in economic evaluation research, but have seldomly been used in chronic pain trials. Both methods provide a single measure between 0 and 1. The relationship between these utility measures and descriptive and domain-specific quality of life measures was examined in 133 fibromyalgia patients and 148 patients with chronic non-specific low back pain. Mean utility score at baseline was 0.43 with the RS and 0.78 for the SG. The correlation between both methods was found to be poor ( r=0.21). Both measures appeared to be fairly stable in a 2-week test-retest period (intra class correlation coefficient (ICC)=0.74 and 0.77). Scores on the description of patient's own health on six domains, global assessment of change and domain specific measures correlated moderately with the RS scores and low with the SG. Multiple regression analyses demonstrated that 32% of the variance in RS values and only 13% of the variance in SG utilities could be explained by domain-specific measures. These results suggest an acceptable construct validity for the RS but insufficient construct validity for the SG. Valuations of ones own health appear only partially to be related to the assessment of the pain-specific measures and measures of distress. It can be concluded that the RS and domain-specific measures assess partly different, but nevertheless complementary aspects of health-related quality of life. It is therefore recommended to include in economic evaluation studies both domain-specific measures and valuation measures. Finally, in chronic musculoskeletal pain patients, RS scores were found to be more responsive in detecting significant changes in preferences than SG scores. For use in patients with chronic musculoskeletal pain, the RS is preferred to the SG for establishing accurate decisions about the impact of new interventions on their health outcomes.

Patient preferences for location of care: implications for regionalization.

Regionalization of high-risk surgical procedures to selected high-volume centers has been proposed as a way to reduce operative mortality. For patients, however, travel to regional centers may be undesirable despite the expected mortality benefit. To determine the strength of patient preferences for local care. Using a scenario of potentially resectable pancreatic cancer and a modification of the standard gamble utility assessment technique, we determined the level of additional operative mortality risk patients would accept to undergo surgery at a local rather than at a distant regional hospital in which operative mortality was assumed to be 3%. We used multiple logistic regression to identify predictors of willingness to accept additional risk. One hundred consecutive patients (95% male, median age 65) awaiting elective surgery at the Veterans Affairs Medical Center in White River Jct., VT. Additional operative mortality risk patients would accept to keep care local. All patients preferred local surgery if the operative mortality risk at the local hospital were the same as the regional hospital (3%). If local operative mortality risk were 6%, which is twice the regional risk, 45 of 100 patients would still prefer local surgery. If local risk were 12%, 23 of 100 patients would prefer local surgery. If local risk were 18%, 18 of 100 patients would prefer local surgery. Further increases in local risk did not result in large changes in the proportion of patients preferring local care. Many patients prefer to undergo surgery locally even when travel to a regional center would result in lower operative mortality risk. Therefore, policy makers should consider patient preferences when assessing the expected value of regionalizing major surgery.

Reliability, validity and responsiveness of two multiattribute utility measures in patients with chronic obstructive pulmonary disease.

The objective of the study was to evaluate the reliability, validity and responsiveness of two generic multiattribute methods for measuring utility for health states: a 15-dimensional (15D) and a five-dimensional method (EuroQol and EQ-TTO). A self-administered questionnaire with both measures was used in 59 outpatients with chronic obstructive pulmonary disease and the findings compared with standard gamble (SG) and time trade-off (TTO) utilities, spirometry and arterial blood gases. Quality of life scores were smallest for EQ-TTO (median 0.73) and highest for SG and TTO (median 0.91 and 0.95 respectively), while 15D gave intermediate values (median 0.80). The test-retest reliability over 14 days was: 15D (p = 0.90) and EQ-TTO (p = 0.73), using Spearman's rank correlation. 15D was better than EQ-TTO at discriminating between groups of patients after reported global rating of change over 12 months (P = 0.004 versus P = 0.09), indicating that 15D was more responsive. The 15D instrument has many attractive properties when compared to the EQ-TTO method, including a better reliability and responsiveness. Validity depends on validation method. The findings in this study indicate that the different utility measures measure different aspects of health-related quality of life (HRQoL). Caution should be taken when choosing utility instruments in cost-utility studies, as this can strongly influence the results.

Measurement of the validity of utility elicitations performed by computerized interview.

The authors evaluate a measure of the validity of utility elicitations and study the potential effects of invalid elicitations on population utility values. The authors used a computerized survey to describe and measure preferences for three common side-effects of anti-psychotic drugs (tardive dyskinesia [TD], akathesia [AKA], pseudo-parkinsonism). The authors compared the validity of elicitations in 41 healthy volunteers to 22 schizophrenic patients. Preferences were measured using visual analog scale (VAS), pair-wise comparison (PWC), and the Standard Gamble (SG) methods. To assess the validity of each groups' responses, the authors compared the consistency of subjects' rank-order of the desirability of states across methods of preferences assessment (CAMPA). All healthy volunteers and 82% of patients completed the computer survey; of these subjects, 97% of healthy volunteers and 70% of patients indicated they thought they understood the task required of them. However, only 78% of healthy subjects and 44% of patients had a consistent rank ordering of preferences among VAS and PWC ratings; only 80% and 61%, respectively, had a consistent rank ordering preferences among SG and PWC ratings. For two of the three health states, inconsistent subjects had statistically higher SG utilities (for TD, 0.94 versus 0.87, and for AKA 0.92 versus 0.86; P < 0.05). The CAMPA test can identify potentially invalid preference ratings. Potentially invalid preference ratings may bias the "population" utilities for health states.

The relationship between descriptive and valuational quality-of-life measures in patients with intermittent claudication.

The study objective was to assess the relationship between descriptive and valuational quality-of-life measures in patients with intermittent claudication. In telephone interviews, 68 patients completed a questionnaire consisting of a descriptive health status measure (RAND 36-Item Health Survey 1.0), and several valuational measures (standard gamble, time tradeoff, rating scale, and McMaster health utility index). All measures demonstrated reduced quality of life in the patients. Scores on the RAND-36 dimensions correlated moderately well with the rating scale and McMaster health utility index (R = 0.37-0.67) but less well with the standard gamble and the time tradeoff (R = 0.10-0.46). Multiple regression analysis demonstrated that 28% of the variance in the time-tradeoff values and 14% of the variance of the standard-gamble utilities could be explained by the best combination of RAND dimensions. These results suggest that answers to descriptive health-status questions cannot reliably predict standard-gamble utilities or time-tradeoff values.