Correcting Biases in Standard Gamble and Time Tradeoff Utilities

The utility assessment method order influences measurement of parents' risk attitude

BACKGROUND

Standard gamble (SG) and time trade-off (TTO) are two methods used for obtaining health utility values (utilities). Whether the order in which the methods are applied alters the relative utilities obtained by each method is unknown.

OBJECTIVE

We sought to determine whether the order in which SG and TTO utilities were obtained affects the relative values of the utilities obtained by each technique.

METHODS

Utilities were assessed for 29 health states from 4016 parents by using SG and TTO. The assessment order was randomized by respondent. For analysis by health state, we calculated (SG - TTO) for each assessment and tested whether the SG - TTO difference was significantly different between the two groups (SG first and TTO first). For analysis by individual, we calculated a risk-posture coefficient, γ, defined by the utility curve, SG = TTO(γ). We predicted γ through regression analysis with the covariates: child age, child sex, birth order, respondent age, respondent education level, and assessment method order.

RESULTS

In 19 of 29 health states, the SG - TTO difference was significantly greater (more risk averse) when TTO was assessed first. In the regression analysis, "child age" and "assessment method order" were significant predictors of risk attitude. The risk posture coefficient γ was higher (more risk-seeking) with increasing child age and in the SG-first respondents.

CONCLUSION

The order in which the SG versus TTO method is used strongly influences the relative values of the utilities obtained.

Construct validity of the interview time trade-off and computer time trade-off in patients with rheumatoid arthritis: a cross-sectional observational pilot study

BACKGROUND

The Time Trade-Off (TTO) is a widely used instrument for valuing preference-based health-related quality of life (HRQoL). The TTO reveals preferences for own current health ('utilities') on a scale anchored between death (0) and perfect health (1). Limited information on the external validity of the TTO is available. Aim of this pilot study was to examine the construct validity of both an interview TTO and a computer-based TTO in patients with rheumatoid arthritis (RA).

METHODS

Thirty patients visiting the outpatient rheumatology clinic participated. Construct validity was assessed by measuring convergent and discriminative validity. Convergent validity was assessed by calculating Spearman's correlations between the utilities obtained from the TTOs and pain, general health (rating scales), health-related quality of life (SF-36 and SF-6D) and functional status (HAQ-DI). Discriminative power of both TTO measures was determined by comparing median utilities between worse and better health outcomes.

RESULTS

Correlations of both TTO measures with HRQoL, general health, pain and functional status were poor (absolute values ranging from .05 to .26). Both TTOs appeared to have no discriminative value among groups of RA patients who had a worse or better health status defined by six health outcome measures. About one-third of respondents were zero-traders on each of the TTO measures. After excluding zero-traders from analysis, the correlations improved considerably.

CONCLUSIONS

Both the interview TTO and computer TTO showed poor construct validity in RA patients when using measures of HRQol, general health, pain and functional status as reference measures. Possibly, the validity of the TTO improves when using an anchor that is more realistic to RA patients than the anchor 'death'.

A direct method for measuring discounting and QALYs more easily and reliably

Time discounting and quality of life are two important factors in evaluations of medical interventions. The measurement of these two factors is complicated because they interact. Existing methods either simply assume one factor given, based on heuristic assumptions, or invoke complicating extraneous factors, such as risk, that generate extra biases. The authors introduce a method for measuring discounting (and then quality of life) that involves no extraneous factors and that avoids distorting interactions. Their method is considerably simpler and more realistic for subjects than existing methods. It is entirely choice based and thus can be founded on economic rationality requirements. An experiment demonstrates the feasibility of this method and its advantages over classical methods.

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.

Are Medical Outcomes Fungible? A Survey of Voters, Medical Administrators, and Physicians

Purpose. Many analyses of medical treatments entail the aggregation of health outcomes over patients and over time. This study assessed the extent to which voters, medical administrators, and physicians consider such aggregation to be appropriate. In addition, the study assessed whether this perceived fungibility of outcomes moderates the difference between treatment recommendations in single-play decisions (for 1 patient on 1 occasion) and those in repeated-play decisions (for several patients or for 1 patient on several occasions). Methods. In a 5-contact mail survey of registered voters ( n = 182, response rate = 52%), medical administrators ( n = 123, 35%), and physicians ( n = 95, 26%), respondents rated the fungibility of outcomes and indicated their preferred action in 1 of 3 scenarios involving changes in life expectancy or the duration of pain. They evaluated a risky, positive-expected-value treatment in a single-play decision, then in a repeated-play decision, and again in a repeated-play decision after they viewed the distribution of possible net outcomes. Results. Perceived fungibility varied substantially across respondents in all groups, with voters giving higher fungibility ratings than administrators or physicians. Respondents’ strength-of-preference ratings for treatment increased from single-play to repeated-play decisions, but these increases were moderated by perceived fungibility, as expected. When outcomes were considered fungible, treatments were much more attractive in repeated-play decisions than in single-play decisions. When outcomes were considered nonfungible, there was essentially no difference between single- and repeated-play decisions. Conclusions. Recommendations regarding risky medical treatments with positive expectations appear to depend, in part, on opinions about whether it is reasonable to aggregate medical outcomes over patients or over time. Such opinions vary widely among physicians and others.

Eliciting Benefit–Risk Preferences and Probability-Weighted Utility Using Choice-Format Conjoint Analysis

This study applies conjoint analysis to estimate health-related benefit-risk tradeoffs in a non-expected-utility framework. We demonstrate how this method can be used to test for and estimate nonlinear weighting of adverse-event probabilities and we explore the implications of nonlinear weighting on maximum acceptable risk (MAR) measures of risk tolerance. We obtained preference data from 570 Crohn’s disease patients using a web-enabled conjoint survey. Respondents were presented with choice tasks involving treatment options that involve different efficacy benefits and different mortality risks for 3 possible side effects. Using conditional logit maximum likelihood estimation, we estimate preference parameters using 3 models that allow for nonlinear preference weighting of risks—a categorical model, a simple-weighting model, and a rank dependent utility (RDU) model. For the second 2 models we specify and jointly estimate 1- and 2-parameter probability weighting functions. Although the 2-parameter functions are more flexible, estimation of the 1-parameter functions generally performed better. Despite well-known conceptual limitations, the simple-weighting model allows us to estimate weighting function parameters that vary across 3 risk types, and we find some evidence of statistically significant differences across risks. The parameter estimates from RDU model with the single-parameter weighting function provide the most robust estimates of MAR. For an improvement in Crohn’s symptom severity from moderate and mild, we estimate maximum 10-year mortality risk tolerances ranging from 2.6% to 7.1%. Our results provide further the evidence that quantitative benefit-risk analysis used to evaluate medical interventions should account explicitly for the nonlinear probability weighting of preferences.

A prospective cohort study defining utilities using time trade-offs and the Euroqol-5D to assess the impact of cancer-related lymphedema

BACKGROUND

The devastating impact of lymphedema on cancer survivors' quality of life has prompted consideration of several changes in medical and surgical care. Unfortunately, our understanding of the benefits gained from these approaches relative to their cost remains limited. This study was designed to estimate utilities for lymphedema and characterize how utilities differ between subgroups defined by lymphedema etiology and distribution.

METHODS

A consecutive sample of 236 subjects with lymphedema seen at a lymphedema clinic completed both a time trade-off (TTO) exercise and the Euroqol 5D. Responses were adjusted in multivariate regression models for demographic factors, comorbidities, and lymphedema severity/location.

RESULTS

Most participants (167 of 236, 71%) had lymphedema as a consequence of cancer treatment; 123 with breast cancer and upper extremity involvement. Mean TTO utility estimates were consistently higher than Euroqol 5D estimates. Unadjusted TTO (0.85; standard deviation [SD], 0.21) and Euroqol 5D (0.76; SD, 0.18) scores diminished with increasing lymphedema stage and patient body mass index (BMI). Adjusted utility scores were lowest in patients with cancer-related lower extremity lymphedema (TTO=0.82; SD, 0.04 and Euroqol 5D=0.80; SD, 0.03). Breast cancer patients also had lower adjusted Euroqol 5D scores (0.80; SD, 0.02).

CONCLUSIONS

Lymphedema-associated utilities are in the range of 0.80. Lower utilities are observed for patients with higher lymphedema stages, elevated BMI, and cancer-related lymphedema. Greater expenditures for the prevention and treatment of cancer-related lymphedema are warranted.

Preference values associated with stage III colon cancer and adjuvant chemotherapy

PURPOSE

To elicit preference values for health states associated with Stage III colon cancer (CRC) and to explore the effect of neuropathy associated with current adjuvant treatment.

METHODS

We used time trade-off (TTO) techniques to elicit preferences from 49 CRC patients and 49 community members. We elicited preferences for 7 health states: remission; adjuvant therapy with no, mild, moderate, and severe neuropathy; metastatic stable; and metastatic progressive disease. Mean TTO values were adjusted for the covariates age, education, and current health.

RESULTS

Patients' adjusted mean TTO value for remission was 0.83; adjuvant chemotherapy health states ranged from 0.48 to 0.61. Significant differences were observed for both patient and community groups between TTO for remission and all adjuvant health states (P < 0.001), and between adjuvant therapy with no neuropathy and metastatic health states (P < or = 0.001). Across all health states, patients' values were on average 0.12 higher than community members (P < 0.05).

CONCLUSIONS

The findings highlight the trade-offs between the disutility of adjuvant treatment, the higher utility of remission, and the severe utility loss during metastatic disease. The preference values obtained from this study will be useful for informing patients' treatment decisions and payer cost-utility analyses of adjuvant treatment for colon cancer.

Analysing risk attitudes to time

The assumption of risk neutrality over discounted life years underlies the standard QALY model of individual preferences over health outcomes, and is thus implicitly assumed by NICE and other health technology advisory bodies worldwide. The primary objective of this article is to report a study to test the assumption in a convenience sample of 30 respondents with use of the probability equivalence version of the standard gamble. The results indicate considerable risk aversion over life years, and therefore call into question the standard assumption of risk neutrality in practical cost-utility analyses (CUA). A secondary objective is to observe whether risk aversion can be reduced through the use of the lottery equivalents method, under the hypothesis that the gambling effect can be lessened with this instrument. In a separate convenience sample of 40 respondents, however, the observed level of risk aversion was at least that seen in the standard gamble. Further research is warranted to ascertain whether risk aversion over discounted life years is a generalisable concern.

The predictive validity of prospect theory versus expected utility in health utility measurement

Most health care evaluations today still assume expected utility even though the descriptive deficiencies of expected utility are well known. Prospect theory is the dominant descriptive alternative for expected utility. This paper tests whether prospect theory leads to better health evaluations than expected utility. The approach is purely descriptive: we explore how simple measurements together with prospect theory and expected utility predict choices and rankings between more complex stimuli. For decisions involving risk prospect theory is significantly more consistent with rankings and choices than expected utility. This conclusion no longer holds when we use prospect theory utilities and expected utilities to predict intertemporal decisions. The latter finding cautions against the common assumption in health economics that health state utilities are transferable across decision contexts. Our results suggest that the standard gamble and algorithms based on, should not be used to value health.

Decision Analysis and Cost-effectiveness Analysis

Healthcare decision-making can be complex, often requiring decision makers to weigh serious trade-offs, consider patients' values, and incorporate evidence in the face of uncertainty. Medical decisions are made implicitly by clinicians and other decision-makers on a daily basis. Decisions based largely on personal experience are subject to many biases. Decision analysis and cost-effectiveness analysis are systematic approaches used to support decision-making under conditions of uncertainty that involve important trade-offs. These mathematical tools can provide patients, physicians and policy makers with a useful approach to complex medical decision making.

The influence of subjective life expectancy on health state valuations using a 10 year TTO

AIM

To investigate if subjective life expectancy (SLE) impacts the willingness to trade-off (WTT) and the number of years traded-off in a 10-years time trade-off (TTO) exercise to obtain health state valuations.

METHODS

An Internet-based questionnaire was administered in a sample representative for the Dutch general public. Next to basic demographic characteristics and SLE, respondents were asked to perform three TTO exercises. The following EQ-5D health states were included 21211 (TTO1), 22221 (TTO2) and 33312 (TTO3). The WTT was studied using a probit regression model. The number of years traded-off was investigated using a generalized negative binomial regression model. The independent variables used in both models were age, gender, quality of life, education, the difference between age and expected age of death (SLE), and a variable indicating whether the SLE was less than 10 years (SLE<10).

RESULTS

Three hundred and thirty nine respondents completed the questionnaire. The mean utility scores were 0.96 (TTO1), 0.94 (TTO2) and 0.79 (TTO3). The probit model showed that SLE was the only variable with a significant influence on WTT. The gnbreg showed that the number of years traded-off was also significantly influenced by SLE. In addition, age and education significantly influenced the number of years traded-off.

CONCLUSION

The WTT years and the number of years traded-off were both influenced by SLE in 10-years TTO exercises. Reducing remaining life expectancy to 10 years in a TTO may thus increase loss aversion and, especially in respondents losing relatively many expected life years, diminish WTT and the amount of time traded off.

The correction of TTO-scores for utility curvature using a risk-free utility elicitation method

This paper describes and employs a new method to correct time tradeoff (TTO)-scores for utility of life duration curvature. In contrast to most previous attempts to do so, it uses a risk-free method that corresponds well to the risk-free properties of the TTO-method. In addition, the method is robust to several biases that occur under methods that incorporate risk. Our results show a significant degree of curvature in utility of life duration and therefore a clear bias in TTO-scores. The risk-free method seems to be useful to correct TTO-scores for this influence and leads to significantly higher quality-adjustment factors.

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.

Health Utility Bias: A Systematic Review and Meta-Analytic Evaluation

Background. A common assertion is that rating scale (RS) values are lower than both standard gamble (SG) and time tradeoff (TTO) values. However, differences among these methods may be due to method specific bias. Although SG and TTOs suffer systematic bias, RS responses are known to depend on the range and frequency of other health states being evaluated. Over many diverse studies this effect is predicted to diminish. Thus, a systematic review and data synthesis of RS-TTO and RS-SG difference scores may better reveal persistent dissimilarities. Purpose. The purpose of this study was to establish through systematic review and meta-analysis the net effect of biases that endure over many studies of utilities. Methods. A total of 2206 RS and TTO and 1318 RS and SG respondents in 27 studies of utilities participated. MEDLINE was searched for data from 1976 to 2004, complemented by a hand search of full-length articles and conference abstracts for 9 journals known to publish utility studies, as well as review of results and additional recommendations by 5 outside experts in the field. Two investigators abstracted the articles. We contacted the investigators of the original if required information was not available. Results. No significant effect for RS and TTO difference scores was observed: effect size (95% confidence interval [CI]) = 0.04 (−0.02, 0.09). In contrast, RS scores were significantly lower than SG scores: effect size (95% CI ) =−0.23 (−0.28, −0.19). Correcting SG scores for 3 known biases (loss aversion, framing, and probability weighting) eliminated differences between RS and SG scores: effect size (95% CI ) = 0.01 (−0.03, 0.05). Systematic bias in the RS method may exist but be heretofore unknown. Bias correction formulas were applied to mean not individual utilities. Conclusions. The results of this study do not support the common view that RS values are lower than TTO values, may suggest that TTO biases largely cancel, and support the validity of formulas for correcting SG bias.

Fitting observed and theoretical choices - women's choices about prenatal diagnosis of Down syndrome

Choices regarding prenatal diagnosis of Down syndrome - the most frequent chromosomal defect - are particularly relevant to decision analysis, since women's decisions are based on the assessment of their risk of carrying a child with Down syndrome, and involve tradeoffs (giving birth to an affected child vs procedure-related miscarriage). The aim of this study, based on face-to-face interviews with 78 women aged 25-35 with prior experience of pregnancy, was to compare the women' expressed choices towards prenatal diagnosis with those derived from theoretical models of choice (expected utility theory, rank-dependent theory, and cumulative prospect theory). The main finding obtained in this study was that the cumulative prospect model fitted the observed choices best: both subjective transformation of probabilities and loss aversion, which are basic features of the cumulative prospect model, have to be taken into account to make the observed choices consistent with the theoretical ones.

Is risk attitude outcome specific within the health domain?

The aim of this study is to examine whether individuals' risk attitude for life years differ from their risk attitude for quality of life. The study also investigates two different framing effects, an order and sequence effect, and the interaction between risk attitude and time preferences. The results showed that individuals tended to be risk averse with respect to the gamble involving risk of immediate death and risk seeking with respect to the other health gambles. Varying the order of the questions or the sequence of full health and ill-health did not seem to systematically bias the estimates.

Health state valuation in mild to moderate cognitive impairment: feasibility of computer-based, direct patient utility assessment

BACKGROUND

Most patients with dementia will, at some point, need a proxy health care decision maker. It is unknown whether persons with various degrees of cognitive impairment can reliably report their health-related preferences.

METHODS

The authors performed health state valuations (HSVs) of current and hypothetical future health states on 47 pairs of patients with mild to moderate cognitive impairment and their caregivers using computer-based standard gamble, time tradeoff, and rating scale techniques.

RESULTS

Patients' mean (SD) age was 74.6 (9.3) years. About half of the patients were women (48%), as were most caregivers (73%), who were on average younger (mean age= 66.2 years, SD= 12.2). Most participants were white (83%); 17% were African American. The mean (SD) Mini-Mental State Examination (MMSE) score of patients was 24.2 (4.6) of 30. All caregivers and 77% of patients (36/47) completed all 18 components of the HSV exercise. Patients who completed the HSV exercise were slightly younger (mean age [SD]= 74.1 [8.5] v. 75.9 [11.8]; P = 0.569) and had significantly higher MMSE scores (mean score [SD] = 25.0 [4.3] v. 21.4 [4.4]; P = 0.018). Although MMSE scores below 20 did not preclude the completion of all 18 HSV ratings, being classified as having moderate cognitive impairment was associated with a lower likelihood of completing all scenario ratings (44% v. 82%). Patient and caregiver responses showed good consistency across time and across techniques and were logically consistent.

CONCLUSION

Obtaining HSVs for current and hypothetical health states was feasible for most patients with mild cognitive impairment and many with moderate cognitive impairment. HSV assessments were consistent and reasonable.

Validity, feasibility and acceptability of time trade-off and standard gamble assessments in health valuation studies: a study in a multiethnic Asian population in Singapore

OBJECTIVES

To assess the validity, feasibility and acceptability of standard gamble (SG) and time trade-off (TTO) assessments in a multiethnic Asian population.

METHODS

Through in-depth interviews performed among Chinese, Malay, and Indian Singaporeans (education >or= 6 years), we assessed validity of SG/TTO methods for eliciting health preferences by hypothesizing that 1) SG/TTO scores for three hypothetical health states (HS) would exhibit ranked order (decreasing scores with worse HS); and 2) more subjects would rate the most severe HS as worse than dead. Subjects also evaluated feasibility and acceptability of SG/TTO using a 10-point visual analog scale (VAS) and open-ended questions. Ratings were compared using Kruskal-Wallis, Wilcoxon signed-rank tests or tests of proportions.

VALIDITY

In 62 subjects (90% response rate), as hypothesized, SG and TTO scores exhibited ranked order with increasing HS severity (SG: 0.85, 0.08, -19.00; TTO: 0.85, 0.00, -0.18). More subjects rated the most severe HS as worse than dead (SG: 8%, 39%, 59%; TTO: 8%, 45% and 62%).

FEASIBILITY

Subjects felt SG and TTO were easy to understand (median VAS scores: 8.0 vs. 8.0, P = 0.87) and to complete (8.0 vs. 8.0, P = 0.84). Acceptability: SG and TTO were well accepted, with TTO less so than SG (median [interquartile range] offensiveness: 2.0 [0, 4.0] vs. 2.0 [0, 3.0], P = 0.045). Overall, subjects did not have a clear preference for SG/TTO (50% vs. 45%, P = 0.70).

CONCLUSIONS

This study suggests the validity, feasibility and acceptability of SG and TTO for population-based HS valuation studies in a multiethnic Asian population.

Reference-dependent preferences and loss aversion: A discrete choice experiment in the health-care sector

This study employs a Discrete Choice Experiment (DCE) in the health-care sector to test the loss aversion theory that is derived from reference-dependent preferences: The absolute subjective value of a deviation from a reference point is generally greater when the deviation represents a loss than when the same-sized change is perceived as a gain. As far as is known, this paper is the first to use a DCE to test the loss aversion theory. A DCE is a highly suitable tool for such testing because it estimates the marginal valuations of attributes, based on deviations from a reference point (a constant scenario). Moreover, loss aversion can be examined for each attribute separately. Another advantage of a DCE is that is can be applied to non-traded goods with non-tangible attributes. A health-care event is used for empirical illustration: The loss aversion theory is tested within the context of preference structures for maternity-ward attributes, estimated using data gathered from 3850 observations made by a sample of 542 women who had recently given birth. Seven hypotheses are presented and tested. Overall, significant support for behavioral loss aversion theories was found.

Health state utilities: a framework for studying the gap between the imagined and the real

OBJECTIVES

Health state utilities play an important role in decision analysis and cost-utility analysis. The question whose utilities to use at various levels of health-care decision-making has been subject of considerable debate. The observation that patients often value their own health, but also other health states, higher than members of the general public raises the question what underlies such differences? Is it an artifact of the valuation methods? Is it adaptation versus poor anticipated adaptation? This article describes a framework for the understanding and study of potential mechanisms that play a role in health state valuation. It aims at connecting research from within different fields so that cross-fertilization of ideas may occur.

METHODS

The framework is based on stimulus response models from social judgment theory. For each phase, from stimulus, through information interpretation and integration, to judgment, and, finally, to response, we provide evidence of factors and processes that may lead to different utilities in patients and healthy subjects.

RESULTS

Examples of factors and processes described are the lack of scope of scenarios in the stimulus phase, and appraisal processes and framing effects in the information interpretation phase. Factors that play a role in the judgment phase are, for example, heuristics and biases, adaptation, and comparison processes. Some mechanisms related to the response phase are end aversion bias, probability distortion, and noncompensatory decision-making.

CONCLUSIONS

The framework serves to explain many of the differences in valuations between respondent groups. We discuss some of the findings as they relate to the field of response shift research. We propose issues for discussion in the field, and suggestions for improvement of the process of utility assessment.

The construction of standard gamble utilities

Health effects for cost-effectiveness analysis are best measured in life years, with quality of life in each life year expressed in terms of utilities. The standard gamble (SG) has been the gold standard for utility measurement. However, the biases of probability weighting, loss aversion, and scale compatibility have an inconclusive effect on SG utilities. We determined their effect on SG utilities using qualitative data to assess the reference point and the focus of attention. While thinking aloud, 45 healthy respondents provided SG utilities for six rheumatoid arthritis health states. Reference points, goals, and focuses of attention were coded. To assess the effect of scale compatibility, correlations were assessed between focus of attention and mean utility. The certain outcome served most frequently as reference point, the SG was perceived as a mixed gamble. Goals were mostly mentioned with respect to this outcome. Scale compatibility led to a significant upward bias in utilities; attention lay relatively more on the low outcome and this was positively correlated with mean utility. SG utilities should be corrected for loss aversion and probability weighting with the mixed correction formula proposed by prospect theory. Scale compatibility will likely still bias SG utilities, calling for research on a correction.

Growth hormone (GH) replacement in hypopituitary adults with GH deficiency evaluated by a utility-weighted quality of life index: a precursor to cost-utility analysis

OBJECTIVES

To examine quality of life (QoL) measured by a utility-weighted index in GH-deficient adults on GH replacement and analyse the impact of demographic and clinical characteristics on changes in utilities during treatment.

DESIGN

Utilities for items in the QoL-Assessment of Growth Hormone Deficiency in Adults (QoL-AGHDA(utility)) were estimated based on data obtained from the general population in England and Wales (E&W). These estimates were used to calculate QoL changes in GH-treated patients and compare these with normative population values.

PATIENTS

A total of 894 KIMS patients (53% women) from E&W were followed for 1 to 6 years.

MEASUREMENTS

QoL-AGHDA(utility) at baseline and at the last reported visit, total QoL-AGHDA(utility) gain and QoL-AGHDA(utility) gain per year of follow-up.

RESULTS

QoL-AGHDA(utility) in patients before GH treatment differed from the expected population values [0.67 (SD 0.174) vs. 0.85 (SD 0.038), P < 0.0001], constituting a mean deficit of -0.19 (SD 0.168). There was a difference in the mean QoL-AGHDA(utility) deficit for men [-0.16 (SD 0.170)] and women [-0.21 (SD 0.162)] (P < 0.001). The main improvement occurred during the first year of treatment [reduction of a deficit to -0.07 (SD 0.163) (P < 0.001) in the total cohort]; however, patients' utilities remained lower than those recorded for the general population during subsequent follow-up (P < 0.001). Despite an observed impact of age, primary aetiology, disease onset and comorbidities on QoL-AGHDA(utility), all patients showed a similar beneficial response to treatment.

CONCLUSIONS

QoL-AGHDA(utility) efficiently monitors treatment effects in patients with GHD. The study confirmed the QoL-AGHDA(utility) deficit before treatment and a similar QoL-AGHDA(utility) gain observed after commencement of GH replacement in all patients.

Patient preference quality of life measures in dermatology

Patient quality of life (QOL) is an important aspect of health care. It is crucial that we continue to develop instruments to assist in detecting burden of disease, interpreting outcomes of clinical trials, determining cost effectiveness of therapies, and guiding clinical decision making. The measurement of patient preferences, specifically utilities and contingent valuation, for health states provides data that can assist in the aforementioned endeavors. Patient preferences have been measured in many areas of medicine. However, it is relatively new to the field of dermatology. The present authors provide an overview of the basic concepts of patient preference measures and how they compare to the widely used health status instruments. Various techniques that have been used to elicit patient preferences are discussed, including standard gamble, time trade-off, willingness-to-pay, rating scales, health utilities index, and EuroQol (EQ-5D). In addition, the present authors review the current literature reporting utilities relevant to dermatology.

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.

Decision curve analysis: a novel method for evaluating prediction models

BACKGROUND

Diagnostic and prognostic models are typically evaluated with measures of accuracy that do not address clinical consequences. Decision-analytic techniques allow assessment of clinical outcomes but often require collection of additional information and may be cumbersome to apply to models that yield a continuous result. The authors sought a method for evaluating and comparing prediction models that incorporates clinical consequences,requires only the data set on which the models are tested,and can be applied to models that have either continuous or dichotomous results.

METHOD

The authors describe decision curve analysis, a simple, novel method of evaluating predictive models. They start by assuming that the threshold probability of a disease or event at which a patient would opt for treatment is informative of how the patient weighs the relative harms of a false-positive and a false-negative prediction. This theoretical relationship is then used to derive the net benefit of the model across different threshold probabilities. Plotting net benefit against threshold probability yields the "decision curve." The authors apply the method to models for the prediction of seminal vesicle invasion in prostate cancer patients. Decision curve analysis identified the range of threshold probabilities in which a model was of value, the magnitude of benefit, and which of several models was optimal.

CONCLUSION

Decision curve analysis is a suitable method for evaluating alternative diagnostic and prognostic strategies that has advantages over other commonly used measures and techniques.

Measuring preferences for cost-utility analysis: how choice of method may influence decision-making

Preferences for health are required when the economic value of healthcare interventions are assessed within the framework of cost-utility analysis. The objective of this paper was to review alternative methods for preference measurement and to evaluate the extent to which the method may affect healthcare decision-making. Two broad approaches to preference measurement that provide societal health state values were considered: (i) direct measurement; and (ii) preference-based health state classification systems. Among studies that compared alternative preference-based systems, the EQ-5D tended to provide larger change scores and more favourable cost-effectiveness ratios than the Health Utilities Index (HUI)-2 and -3, while the SF-6D provided smaller change scores and less favourable ratios than the other systems. However, these patterns may not hold for all applications. Empirical evidence comparing systems and decision-making impact suggests that preferences will have the greatest impact on economic analyses when chronic conditions or long-term sequelae are involved. At present, there is no clearly superior method, and further study of cost-effectiveness ratios from alternative systems is needed to evaluate system performance. Although there is some evidence that incremental cost-effectiveness ratio (ICER) thresholds (e.g. $US50,000 per QALY gained) are used in decision-making, they are not strictly applied. Nonetheless, as ICERs rise, the probability of acceptance of a new therapy is likely to decrease, making the differences in QALYs obtained using alternative methods potentially meaningful. It is imperative that those conducting cost-utility analyses characterise the impact that uncertainty in health state values has on the economic value of the interventions studied. Consistent reporting of such analyses would provide further insight into the policy implications of preference measurement.

The influence of the ratio bias phenomenon on the elicitation of health states utilities

This paper tests whether logically equivalent risk formats can lead to different health state utilities elicited by means of the traditional standard gamble (SG) method and a modified version of the method that we call “double lottery.” We compare utilities for health states elicited when probabilities are framed in terms of frequencies with respect to 100 people in the population (i.e., X out of 100 who follow a medical treatment will die) with SG utilities elicited for frequencies with respect to 1,000 people in the population (i.e., Y out of 1,000 who follow a medical treatment will die). We found that people accepted a lower risk of death when success and failure probabilities were framed as frequencies type “Y deaths out of 1,000” rather than as frequencies type “X deaths out of 100” and hence the utilities for health outcomes were higher when the denominator was 1000 than when it was 100. This framing effect, known as Ratio Bias, may have important consequences in resource allocation decisions.

A test of prospect theory

Objectives: Prospect theory (PT) hypothesizes that people judge states relative to a reference point, usually assumed to be their current health. States better than the reference point are valued on a concave portion of the utility function; worse states are valued on a convex portion. Using prospectively collected utility scores, the objective is to test empirically implications of PT.

Methods: Osteoarthritis (OA) patients undergoing total hip arthroplasty periodically provided standard gamble scores for three OA hypothetical states describing mild, moderate, and severe OA as well as their subjectively defined current state (SDCS). Our hypothesis was that most patients improved between the pre- and postsurgery assessments. According to PT, scores for hypothetical states previously > SDCS but now < SDCS should be lower at the postsurgery assessment.

Results: Fourteen patients met the criteria for testing the hypothesis. Predictions were confirmed for 0 patients; there was no change or mixed results for 6 patients (42.9 percent); and scores moved in the direction opposite to that predicted by PT for 8 patients (57.1 percent).

Conclusions: In general, the direction and magnitude of the changes in hypothetical-state scores do not conform to the predictions of PT.

Measuring utilities by the time trade-off method in Tunisian rheumatoid arthritis patients

The objective of this study was to determine the feasibility, reliability and validity of the time trade-off (TTO) in Tunisian rheumatoid arthritis (RA) patients. The TTO was used to measure the utility in 122 RA patients with increasing difficulty in performing activities of daily living. The 1-week test-retest reproducibility was studied in 57 patients using the intraclass correlation coefficient (ICC). Validity was evaluated by comparison with other outcome measures: utility rating scale (RS), quality of life (QOL) [arthritis impact measurement scale 2 (AIMS2), rheumatoid arthritis quality of life (RAQOL)], functional status [health assessment questionnaire (HAQ), Lee index] and disease activity score (DAS). Eight patients (6.6%) did not complete the TTO. The median value of the TTO score was 0.655 (0.019-1.000). The ICC for reliability of the TTO was 0.89 (p<0.001). The TTO showed poor to moderate correlation (Spearman's correlation coefficients between 0.2 and 0.409, p<0.01) with AIMS2, RAQOL, HAQ and Lee index. We did not find any correlation between TTO and DAS. Multiple regression analysis showed that only 32% of TTO scores could be explained. The TTO method appeared to be reliable in a group of Tunisian RA patients, but TTO values were poorly to moderately related to measures of QOL, functional ability, and disease activity. We think that TTO and RS are not feasible for use in RA patients.

Health-state valuations for pertussis: methods for valuing short-term health states

BACKGROUND

The incidence of reported adolescent and adult pertussis continues to rise in the United States. Acellular pertussis vaccines for adolescents and adults have been developed and may be available soon for use in the U.S. Our objectives were: (1) to describe patient valuations of pertussis disease and vaccination; and (2) to compare valuations for short-term and long-term health states associated with pertussis.

METHODS

We conducted telephone surveys with 515 adult patients and parents of adolescent patients with pertussis in Massachusetts to determine valuations of pertussis-related health states for disease and vaccination using time trade-off (TTO) and contingent valuation (CV) techniques. Respondents were randomized to complete either a short-term or long-term TTO exercise. Discrimination between health states for each valuation technique was assessed using Tukey's method, and valuations for short-term vs. long-term health states were compared using the Wilcoxon rank-sum test.

RESULTS

Three hundred three (59%) and 309 (60%) respondents completed and understood the TTO and CV exercises, respectively. Overall, respondents gave lower valuations (lower TTO and higher CV values) to avoid a given state for adolescent/adult disease compared to vaccine adverse events. Infant complications due to pertussis were considered worse than adolescent/adult disease, regardless of the method of valuation. The short-term TTO resulted in lower mean valuations and larger mean differences between health states than the long-term TTO exercise.

CONCLUSION

Pertussis was considered worse than adverse events due to vaccination. Short-term health-state valuation is better able to discriminate among health states, which is useful for cost-utility analysis.