Parameter estimates for a QALY utility model

An experimental investigation of social risk preferences for health

In this paper, we use the risk apportionment technique of Eeckhoudt, Rey and Schlesinger (2007) to study higher order risk preferences for others' health as well as ex-ante and ex-post inequality preferences for social risky distributions, and their interaction. In an experiment on a sample of university students acting as impartial spectators, we observe risk aversion towards social health losses and a dislike of ex-ante inequality. In addition, evidence for ex-post inequality seeking is much weaker than evidence for ex-ante inequality aversion. Because ex-ante inequality aversion is unrelated to risk aversion, we conclude that simple forms of utilitarianism are not relevant for individual judgment of social risk over health. Last, our investigation of precautionary distribution, which would occur when one particular group in the society suffers from background health risk, shows substantial polarization of preferences.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11238-023-09928-w.

Trends in the cost-effectiveness level of percutaneous coronary intervention: Macro socioeconomic analysis and health technology assessment

Percutaneous coronary intervention (PCI), one of the most prevalent techniques of revascularization, is a procedure that remarkably improves treatment outcomes. However, it consumes large amounts of medical resources and has resulted in an increased socioeconomic burden due to the increasing number of target patients. In recent years, there have been sporadic discussions, both in Japan and other countries, regarding the optimization of interventions and the perspective of medical economics. Based on this, previous studies on PCI-related cost-effectiveness were reviewed in order to consider the current level of medical economics regarding PCI. Using the databases MEDLINE and EMBASE, a survey involving data from original articles and systematic reviews was conducted from January 2010 to August 2022. Conditions were not imposed on the evidence level due to the paucity of studies, although field studies were prioritized over simulation studies. The macro medical economics of acute myocardial infarction treatment, which is the primary target of PCI, were generally at an average level when compared to those in other countries; however, there is room for further improvement in Japan's performance. Revascularization in a population with multivessel coronary artery disease showed that coronary artery bypass graft surgery tended to be more cost-effective than PCI in the long-term setting. However, it was suggested that PCI may be more cost-effective in patients with SYNTAX Score ≤22 or left main artery disease. A cost-effectiveness report for stable angina patients was not in favor of PCI over medical therapy. Moreover, there were some reports showing the medical economic superiority of early myocardial ischemia evaluation, and it was foreseen that active selection of patients will contribute to the improvement of the overall cost-effectiveness of PCI. In order to further improve the socioeconomic significance of PCI in the future, it is necessary to aim for harmony between clinical practice and health economics.

Comparing the cost-effectiveness of the Otago Exercise Programme among older women and men: A secondary analysis of a randomized controlled trial

Objective

Using stratified analyses, we examined the cost-effectiveness of the Otago Exercise Programme (OEP), from a health care system perspective, among older women and men who have previously fallen.

Methods

This study was a secondary stratified analysis (by women and men), of a 12-month prospective economic evaluation of a randomized clinical trial (OEP compared with usual care). Three hundred and forty four community-dwelling older adults (≥70; 172 OEP (110 women; 62 men), 172 usual care (119 women; 53 men)) who sustained a fall in the past 12 months and received a baseline assessment at the Vancouver Falls Prevention Clinic, Canada were included. A gender by OEP/usual care interaction was examined for the falls incidence rate ratio (IRR). Outcome measures stratified by gender included: falls IRR, incremental cost-per fall prevented (ICER), incremental cost per quality adjusted life year (QALY, ICUR) gained, and mean total health care resource utilization costs.

Results

Men were frailer than women at baseline. Men incurred higher mean total healthcare costs $6794 (SD: $11906)). There was no significant gender by OEP/usual care interaction on falls IRR. The efficacy of the OEP did not vary by gender. The adjusted IRR for the OEP group demonstrated a 39% (IRR: 0.61, CI: 0.40–0.93) significant reduction in falls among men but not women (32% reduction (IRR: 0.69, CI: 0.47–1.02)). The ICER showed the OEP was effective in preventing falls and less costly for men, while it was costlier for women by $42. The ICUR showed the OEP did not impact quality of life.

Conclusion

Future studies should explore gender factors (i.e., health seeking behaviours, gender related frailty) that may explain observed variation in the cost-effectiveness of the OEP as a secondary falls prevention strategy.

Trial registrations

ClinicalTrials.gov Protocol Registration System

Identifier: NCT01029171; URL: https://clinicaltrials.gov/ct2/show/NCT01029171

Identifier: NCT00323596; URL: https://clinicaltrials.gov/ct2/show/NCT00323596

A Head-to-Head Comparison of the Standard Quality-Adjusted Life Year Model With the Annual Profile Model

OBJECTIVES

The standard quality-adjusted life year (QALY) model (SQM) assumes time-utility independence within constant health states and additive independence when health varies over time. The validity of SQM has been challenged through reported violations of these assumptions. An alternative approach that relaxes these assumptions is to assign a single valuation to an entire health profile: an integral assessment of disease severity over time. Here, we compare SQM with the annual profile model (APM) and test SQM for additive independence.

METHODS

Eighty-two respondents valued 6 episodic conditions, including 4 of short duration, with SQM and APM, using the time trade-off method. Inter-rater reliability was assessed using intraclass correlation coefficients. Face validity was tested by asking respondents how well they were able to imagine the health states under SQM and APM. We calculated SQM QALY values for a 1-year time period, allowing for a direct comparison with APM values. For the short-term conditions we expected higher QALY values for SQM, violating additive independence.

RESULTS

APM showed higher interrater reliability (intraclass correlation coefficient of 0.53 vs 0.18, respectively) and better face validity than SQM, with 6% (APM) vs 21% (SQM) of all respondents reporting difficulties. Additive independence of SQM was violated in 5 of the 6 conditions (including the 4 short duration health states), with higher QALY values under SQM (mean difference 0.04).

CONCLUSION

The impact of short-term conditions is systematically underestimated under SQM when compared to a health profile model. APM is a less restrictive model and demonstrates better validity.

An overview of the time trade-off method: concept, foundation, and the evaluation of distorting factors in putting a value on health

INTRODUCTION

Preference-based instruments measuring health status express the value of specific health states in a single number. One method used is time trade-off (TTO). Health-status values are key elements in calculating quality-adjusted life years (QALYs) and are pertinent for resource allocation. Since they are used in economic evaluations of healthcare, searching for a theoretical foundation of TTO in economics is justified.

AREA COVERED

This paper provides an overview of TTO, including its relation to economic theory, and discusses biases and distortions, compiled from recent and older research. Inconsistencies between TTO and random utility theory were detected; The TTO is confounded by time preferences and by respondents' life expectancies. TTO is cognitively challenging, therefore guidance during the interviews is needed, producing interview effects. TTO does not measure one thing at a time, nor are the values independent of other states that are being valued in the same task. That is, TTO does not exhibit theoretical measurement properties such as unidimensionality and the invariance principle.

EXPERT OPINION

We conclude that the TTO may be a pragmatic method of eliciting health state values, but the limitations in regard to measurement theory and practical elicitation problems makes it prone to inconsistencies and arbitrariness.

Action Seniors! Cost-Effectiveness Analysis of a Secondary Falls Prevention Strategy Among Community-Dwelling Older Fallers

BACKGROUND

The Otago Exercise Program (OEP) has demonstrated cost-effectiveness for the primary prevention of falls in a general community setting. The cost-effectiveness of exercise as a secondary falls prevention (ie, preventing falls among those who have already fallen) strategy remains unknown. The primary objective was to estimate the cost-effectiveness (incremental cost-effectiveness/utility ratio) of the OEP from a healthcare system perspective.

DESIGN

A concurrent 12-month prospective economic evaluation conducted alongside the Action Seniors! randomized critical trial (OEP compared with usual care).

SETTING

Vancouver Falls Prevention Clinic (Vancouver, BC, Canada; http://www.fallsclinic.ca).

PARTICIPANTS

A total of 344 community-dwelling older adults, aged 70 years and older, who attended a geriatrician-led Falls Prevention Clinic in Vancouver, after sustaining a fall in the previous 12 months.

MEASUREMENTS

Main outcome measures included: incidence rate ratio for falls, healthcare costs, incremental cost per fall prevented, and incremental cost per quality-adjusted life year (QALY) gained.

RESULTS

The OEP costs $393 CAD per participant to implement. The incremental cost per fall prevented resulted in a savings of $2 CAD. The incremental cost per QALY gained (where QALYs were estimated using the Euro-Qol 5D three-level version [EQ-5D-3L]) indicated the OEP was less effective than usual care. The incremental cost per QALY gained (where QALYs were estimated using the Short Form 6D [SF-6D]) indicated the OEP was more effective and less costly than usual care. The incremental QALYs estimated using the EQ-5D-3L and the SF-6D were not clinically significant and close to zero, indicating no change in quality of life.

CONCLUSION

Compared with usual care, healthcare system costs are saved and falls are prevented when older fallers who attend a geriatrician-led falls clinic are allocated to, and provided, the physiotherapist-guided exercise-based falls prevention program (the OEP).

Preference-Sensitive Management of Post-Mammography Decisions in Breast Cancer Diagnosis

Decision models representing the clinical situations where treatment options entail a significant risk of morbidity or mortality should consider the variations in risk preferences of individuals. In this study, we develop a stochastic modeling framework that optimizes risk-sensitive diagnostic decisions after a mammography exam. For a given patient, our objective is to find the utility maximizing diagnostic decisions where we define the utility over quality-adjusted survival duration. We use real data from a private mammography database to numerically solve our model for various utility functions. Our choice of utility functions for the numerical analysis is driven by actual patient behavior encountered in clinical practice. We find that invasive diagnostic procedures such as biopsies are more aggressively used than what the optimal risk-neutral policy would suggest, implying a far-sighted (or equivalently risk-seeking) behavior. When risk preferences are incorporated into the clinical practice, policy makers should bear in mind that a welfare loss in terms of survival duration is inevitable as evidenced by our structural and empirical results.

Do Risk Attitudes Differ across Domains and Respondent Types?

Objective . To evaluate differences in risk attitude across the domains of health and money for 2 types of respondents, patients and community members. Methods . Two groups of respondents, patients with multiple sclerosis (n = 56) and members of the general community (n = 57), completed a survey that collected information on risk attitudes and socioeconomic and clinical variables (e.g., disability level). Risk attitude was measured using 2 standard-gamble questions on money and 1 standard-gamble question on health outcomes. Multivariate regression was used to evaluate the relationship between risk attitude and respondent type (patient v. community), adjusting for covariates that could affect risk attitude. Results . The median certainty equivalents for money gambles were significantly different from and less than the expected value of the gamble for both types of respondents. Median certainty equivalents for the health gamble were not significantly different from the expected value for either group of respondents. For all 3 gambles, there was no difference in median certainty equivalents between the 2 types of respondents in both unadjusted and adjusted analyses. Conclusions . Risk attitude varied across domains but not by respondent type. Patients and community members were predominantly risk neutral with respect to health outcomes and risk averse with respect to money. Research on risk preferences on money outcomes may not be an appropriate proxy for risk preferences regarding health outcomes. Risk preferences may depend more on characteristics of the choice than on respondent type.

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) tomeasure 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.

Correcting Biases in Standard Gamble and Time Tradeoff Utilities

The standard gamble (SG) method and the time tradeoff (TTO) method are commonly used tomeasure utilities. However, they are distorted by biases due to loss aversion, scale compatibility, utility curvature for life duration, and probability weighting. This article applies corrections for these biases and provides new data on these biases and their corrections. The SG and TTO utilities of 6 rheumatoid arthritis health states were assessed for 45 healthy respondents. Various corrections of utilities were considered. The uncorrected TTO scores and the corrected (for utility curvature) TTO scores provided similar results. This article provides arguments suggesting that the TTO scores are biased upward rather than having balanced biases. The only downward bias in TTO scores was small and probably cannot offset the upward biases. TheTTOscores are higher than the theoretically most preferred correction of the SG, the mixed correction. These findings suggest that uncorrected SG scores, which are higher than TTO scores, are too high.

Health state utilities in non-small cell lung cancer: An international study

AIM

Quality of life weights (utilities) are an important input in economic evaluation and evidence suggests that there can be important differences between countries. This study was designed to capture utilities for metastatic non-small cell lung cancer and common grade III/IV toxicities associated with treatment from local populations in the United Kingdom, Australia, France, China, Taiwan, and Korea. Toxicities included neutropenia, febrile neutropenia, fatigue, diarrhea, nausea and vomiting, rash, bleeding, hypertension, and hair loss.

METHODS

Existing health state descriptions of non-small cell lung cancer were adapted to represent descriptions of patients on first-line treatment. Twenty-three states were translated and assessed in cognitive debrief content validation interviews with oncologists in each country. Seventy-five respondents per country completed a time trade-off interview to evaluate the states. Variation between countries for all states was explored with a Generalized Estimating Equations model.

RESULTS

The mean utility for "stable disease and no side effects" (base state) varied between 0.84 (United Kingdom) and 0.54 (Taiwan). The largest utility decrements were found for febrile neutropenia (0.47) and neutropenia (0.35) across all countries. Asian countries regarded bleeds as a severe toxicity whereas non-Asian countries did not and valued diarrhea and fatigue as more severe. Significant differences in utilities between countries emerged with the Taiwanese population in particular rating states as significantly worse than other countries.

CONCLUSION

This study improves our understanding of how utilities for the same states can vary across countries. The study shows the importance of capturing utilities that reflect the preferences of the local population.

Q-TWiST analysis of panitumumab plus FOLFOX4 versus FOLFOX4 alone in patients with previously untreated wild-type RAS metastatic colorectal cancer

INTRODUCTION

Panitumumab plus infusional 5-fluorouracil, leucovorin, and oxaliplatin (FOLFOX4) significantly improved overall survival versus FOLFOX4 alone in patients with previously untreated wild-type RAS metastatic colorectal cancer (mCRC). We applied a quality-adjusted time without symptoms of disease or toxicity (Q-TWiST) analysis to provide an integrated measure of clinical benefit, with the objective of comparing quality-adjusted survival between the two arms. We acknowledge that there are limitations associated with Q-TWIST methodology for crossover trials.

METHODS

For each treatment arm, the truncated mean times spent in the toxicity (TOX: grade 3 or 4 adverse events), time without symptoms of disease or toxicity (TWiST), and relapse (REL: after disease progression) states were estimated by the product-limit method, and adjusted using utility weights derived from patient-reported EuroQol 5-dimension measures. Sensitivity analyses were performed in which utility weights (varying from 0 to 1) were applied to time in the TOX and REL health states.

RESULTS

Quality-adjusted overall survival time was statistically significantly longer with panitumumab plus FOLFOX4 (20.5 months) than with FOLFOX4 alone (18.2 months) (P = 0.025).

CONCLUSION

In patients with previously untreated wild-type RAS mCRC, panitumumab plus FOLFOX4 significantly improved quality-adjusted survival compared with FOLFOX4 alone.

Are people consistent when trading time for health?

The conventional, or standard, time trade-off (TTO) procedure, which is used to elicit the values that people place on health states that are in turn required to calculate quality adjusted life-years (QALYs), asks respondents to trade off fewer life years for better health. It is possible to reverse the procedure to ask respondents to trade off less health for more life years. Theoretically, these two procedures should generate the same TTO values for any given health state. This article reports that for health states defined by differing frequencies of migraine attack, the standard TTO gives health state values that are significantly higher than those given by the reverse TTO. The observed systematic procedural invariance, which substantiates some previous findings reported in the literature and is consistent with a loss aversion effect, challenges the validity of the TTO for generating reliable valuations of health states.

Deriving time discounting correction factors for TTO tariffs

The Time Trade-off (TTO) method is a popular method for valuing health state utilities and is frequently used in economic evaluations. However, this method produces utilities that are distorted by several biases. One important bias entails the failure to incorporate time discounting. This paper aims to measure time discounting for health outcomes in a sample representative for the general population. In particular, we estimate TTO scores alongside time discounting in order to derive a set of correction factors that can be employed to correct raw TTO scores for the downward bias caused by time discounting. We find substantial positive correction factors, which are increasing with the severity of the health state. Furthermore, higher discounting is found when using more severe health states in the discounting elicitation task. More research is needed to further develop discount rate elicitation procedures and test their validity, especially in general public samples. Moreover, future research should investigate the correction of TTO values for other biases as well, such as loss aversion, and to develop a criterion to test the external validity of TTO scores.

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.

A Q-TWiST analysis comparing panitumumab plus best supportive care (BSC) with BSC alone in patients with wild-type KRAS metastatic colorectal cancer

Background:

Panitumumab+best supportive care (BSC) significantly improved progression-free survival (PFS) vs BSC alone in patients with chemo-refractory wild-type KRAS metastatic colorectal cancer (mCRC). We applied the quality-adjusted time without symptoms of disease or toxicity (Q-TWiST) analysis to provide an integrated measure of clinical benefit, with the objective of comparing quality-adjusted survival between the two arms. As the trial design allowed patients on BSC alone to receive panitumumab after disease progression, which confounded overall survival (OS), the focus of this analysis was on PFS.

Methods:

For each treatment group, the time spent in the toxicity (grade 3 or 4 adverse events; TOX), time without symptoms of disease or toxicity (TWiST), and relapse (after disease progression; REL) states were estimated by the product-limit method, and adjusted using utility weights derived from patient-reported EuroQoL 5-dimensions measures. Sensitivity analyses were performed in which utility weights (varying from 0 to 1) were applied to time in the TOX and REL health states.

Results:

There was a significant difference between groups favouring panitumumab+BSC in quality-adjusted PFS (12.3 weeks vs 5.8 weeks, respectively, P<0.0001) and quality-adjusted OS (P=0.0303).

Conclusion:

In patients with chemo-refractory wild-type KRAS mCRC, panitumumab+BSC significantly improved quality-adjusted survival compared with BSC alone.

Increasing marginal utility of small increases in life-expectancy? Results from a population survey

The standard practice in cost-effectiveness analyses of health care is to assign a linear value to increasing lifetime gains. The aim of the current study was to examine the possible existence of non-linear utility for short life extensions. A representative sample of the Norwegian population, aged 40-59 years (n=2402), was asked to imagine that they had a limited remaining lifetime (1 year or 10 years) and were offered a treatment that would increase lifetime by a specified amount of time from 1 week to 1 year. In all scenarios, the price per week of life extension was held constant. The proportion of respondents that accepted the treatment increased with increasing extensions, indicating a convex utility function. The result suggests increasing marginal utility for life extensions up to 1 year.

A note on the nature of utility in time and health and implications for cost utility analysis

Time Trade-Off (TTO) valuations of health are widely used in economic evaluation of health care. Current approaches to eliciting TTO values, and their use in economic evaluation, rest on specific assumptions about the way utility relates to time and health. Both the assumptions themselves and evidence of violations of them are discussed in the literature - yet the issues appear not to be widely appreciated by those using and applying TTO in economic evaluation. This paper adds to that literature by demonstrating both the requirements of TTO and violations of these assumptions in terms of the underlying indifference curve maps and utility functions. The advantage of this approach is that it demonstrates very clearly a number of fundamental problems for the way TTO values are currently elicited and used in cost utility analysis. In essence, it is extremely unwise to assume that the current 'tariffs' of TTO values, such as those widely used in cost utility analysis to inform health sector decisions in many countries can be applied irrespective of the duration of the health states to which they are assigned. The estimates of QALYs that result will, quite often, simply be wrong. We conclude by pointing to a number of possible solutions.

The Cost of Uncertain Life Span

A considerable amount of uncertainty surrounds the length of human life. The standard deviation in adult life span is about 15 years in the U.S., and theory and evidence suggest it is costly. I calibrate a utility-theoretic model of preferences over length of life and show that one fewer year in standard deviation is worth about half a mean life year. Differences in the standard deviation exacerbate cross-sectional differences in life expectancy between the U.S. and other industrialized countries, between rich and poor countries, and among poor countries. Accounting for the cost of life-span variance also appears to amplify recently discovered patterns of convergence in world average human well-being. This is partly for methodological reasons and partly because unconditional variance in human length of life, primarily the component due to infant mortality, has exhibited even more convergence than life expectancy.

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.

The value of vision

BACKGROUND

The value of vision is assumed to be very high. To verify this assumption and to assign resources in medical care accordingly, it is necessary to quantify the value of vision. Although the value of vision is difficult to measure, visual quality of life can be quantified as a surrogate criterion. The measured value gains even more relevance if a comparison can be made between visual quality of life and systemic diseases. Multidisciplinary comparisons are only possible by using utility analysis. Two established methods to measure utility values are the standard gamble method and the time trade-off method. The purpose of this review is to find ophthalmologic utility values, and utility values affected by systemic diseases that correlate to the ophthalmologic ones.

METHODS

A literature search was conducted through PubMed of the National Library of Medicine ( http://www.ncbi.nlm.nih.gov ; date: 06.02.2006). The search terms were: "time trade-off / standard gamble" [text word] and "eye / vision / visual" [text word]; results 24. A report was classified as relevant if visually impaired persons were tested by the time trade-off method or the standard gamble method, or if information was provided on the reliability and validity of these measurements in a group of visually impaired persons. Additional searches were done to find associated publications. A total of 42 publications were found to be of interest.

RESULTS

Results showed that patients, with 20/30-20/50 visual acuity would be willing to pay 19% of their lifetime to get back normal visual acuity. Patients with 20/200-20/400 visual acuity would give up 48% of their lifetime, and blind people would give 60% of their lifetime to regain normal visual acuity. Comparable utility values are seen in patients with AIDS (21%), patients after a stroke who are unable to walk and wash themselves without assistance (46%), and bedridden and incontinent patients following a stroke (66%).

CONCLUSION

Patients attach great value to vision. The time trade-off method appears to be an appropriate tool to quantify visual quality of life, and one that can be used to compare utility values of different diseases.

Age-related macular degeneration: economic burden and value-based medicine analysis

It can be estimated that 17,100 new cases of neovascular (wet) AMD and 180,000 new cases of geographic-atrophy (dry) AMD occur in Canada annually. In addition to having a devastating effect on patients' lives, the condition causes significant adverse consequences for the economy. The deleterious effect of AMD on quality of life is markedly underestimated by ophthalmologists who treat patients with AMD, by non-ophthalmic physicians and by the public. In fact, patients with different degrees of severity of AMD have a perceived impairment of their quality of life that is 96% to 750% greater than the impairment estimated by treating ophthalmologists. Mild AMD causes a 17% decrease in the quality of life of the average patient, a decrease similar to that encountered with symptomatic human immunodeficiency virus infection or moderate cardiac angina. Moderate AMD produces a 40% decrease in quality of life, a decrease similar to that associated with permanent renal dialysis or severe cardiac angina. Very severe AMD causes a 63% decrement in quality of life, a decrease similar to that encountered with advanced prostatic cancer with uncontrollable pain or a severe stroke that leaves a person bedridden, incontinent and requiring constant nursing care. The adverse economic consequences of AMD include an annual $2.6 billion negative impact on Canada's gross domestic product. The return on investment is high for both current AMD therapies and research into new treatment modalities.

Towards a better QALY model

This paper presents a test of the predictive validity of various classes of QALY models (i.e. linear, power and exponential models). We first estimated TTO utilities for 43 EQ-5D chronic health states and next these states were embedded in nonchronic health profiles. The chronic TTO utilities were then used to predict the responses to TTO questions with nonchronic health profiles. We find that the power QALY model clearly outperforms linear and exponential QALY models. Optimal power coefficient is 0.65. Our results suggest that TTO-based QALY calculations may be biased. This bias can be corrected using a power QALY model.

Quality-adjusted life years: how useful in medico economic studies

Cost-effectiveness analysis has evolved as a practical response to the need to allocate limited resources for health care. It can be used to compare interventions whose effects on health are different if the measure of effectiveness captures all the important health dimensions of the effects of the interventions. Using the quality-adjusted life year (QALY) as the unit of effectiveness attempts to approach this ideal and is currently the approach recommended by many consensus groups. Conventional QALYs represent time spend in a series of "quality-weighted" health states, where the quality weights reflect the desirability of living in the state. Many challenges arise when preferences are incorporated into an economic analysis. The purpose of this paper is to highlight some of the issues surrounding the use of QALYs and to encourage researchers to present their methodology in a clear and transparent way.

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, are affected by loss aversion and lead to utilities that are too high.

Quality of life associated with visual loss: a time tradeoff utility analysis comparison with medical health states

PURPOSE

To assess the visual utility values of patients with ocular disease and to compare these values with those of patients with systemic health states

DESIGN

Cross-sectional utility value assessment.

METHODS

Consecutive patients with ophthalmic diseases were interviewed in a one-on-one fashion using a standardized time tradeoff utility value assessment form. These values were compared with utility values for systemic health states present in the literature.

INTERVENTION

None.

MAIN OUTCOME MEASURE

Time tradeoff utility value on a scale ranging from 1.0 (perfect visual health) to 0.0 (death). The ophthalmic patient groups were stratified into 4 visual groups dependent on the visual acuity in the better-seeing eye. The groups were as follows: group 1, 20/20 to 20/25; group 2, 20/30 to 20/50; group 3, 20/60 to 20/100; group 4, 20/200 to no light perception.

RESULTS

A total of 500 subjects were enrolled in the study. The mean utility values for the visually stratified groups were: group 1, 0.88; group 2, 0.81; group 3, 0.72; group 4, 0.61. Comparable respective systemic health state utility values for each of the ophthalmic groups were: diabetes mellitus, status after kidney transplantation, moderate stroke, and moderately severe stroke.

CONCLUSIONS

Visual loss is associated with a substantial and measurable diminution in quality of life. This diminution in quality of life can be directly compared with that induced by systemic health states.

The validity of time trade-off values in calculating QALYs: constant proportional time trade-off versus the proportional heuristic

In order to calculate quality adjusted life years (QALYs) from time trade-off (TTO) responses, individual preferences are required to satisfy the constant proportional time trade-off (CPTTO) assumption. Respondents who use a simple proportional heuristic may appear to satisfy CPTTO but will in fact generate preference reversals for states that are associated with a maximal endurable time (MET). Using data from 91 respondents, the study reported here examines the extent to which valuations satisfy the CPTTO assumption and the extent to which they might be generated by the proportional heuristic. The results suggest that respondents are using a proportional heuristic that casts doubt on the validity of using the TTO method to calculate QALYs for health states that are associated with MET preferences.

A utility-theoretic model for QALYs and willingness to pay

Despite the widespread use of quality-adjusted life years (QALY) in economic evaluation studies, their utility-theoretic foundation remains unclear. A model for preferences over health, money, and time is presented in this paper. Under the usual assumptions of the original QALY-model, an additive separable presentation of the utilities in different periods exists. In contrast to the usual assumption that QALY-weights do solely depend on aspects of health-related quality of life, wealth-standardized QALY-weights might vary with the wealth level in the presented extension of the original QALY-model resulting in an inconsistent measurement of QALYs. Further assumptions are presented to make the measurement of QALYs consistent with lifetime preferences over health and money. Even under these strict assumptions, QALYs and WTP (which also can be defined in this utility-theoretic model) are not equivalent preference-based measures of the effects of health technologies on an individual level. The results suggest that the individual WTP per QALY can depend on the magnitude of the QALY-gain as well as on the disease burden, when health influences the marginal utility of wealth. Further research seems to be indicated on this structural aspect of preferences over health and wealth and to quantify its impact.

The relationship between risk attitude and treatment choice in patients with relapsing-remitting multiple sclerosis

BACKGROUND

Many patients with multiple sclerosis (MS) eligible for beta-interferons or glatiramer acetate have chosen to forgo or discontinue treatment The objective of this study was to evaluate risk attitude as a patient characteristic related to treatment choice for patients with MS.

METHODS

Sixty-two MS patients completed a survey on treatment history, risk preference, and socioeconomic and clinical variables. Multinomial logistic regression was used to assess the relationship between treatment choice and risk attitude. Risk attitude was measured using a standard gamble question on short-term health outcomes.

RESULTS

More risk-seeking patients were less likely to choose treatment compared with more risk-averse patients (P < 0.01). Forpatients who discontinued treatment, the explanatory variable of significance was severity of side effects (P < 0.05).

CONCLUSIONS

Risk attitude is a patient characteristic related to treatment initiation in patients with MS. This could be an important factor to consider when identifying optimal treatment decisions for individual patients.

QALYs versus WTP

Quality adjusted life years (QALYs) and willingness to pay (WTP) are alternative measures of the value of reductions in health risk that are often used in evaluating environmental, health, and safety practices. Although both methods are based on individual preferences, the underlying assumptions differ. The different bases yield systematically different conclusions about the relative value of reducing health and mortality risks to individuals that differ in age, preexisting health conditions, income, and other factors. The choice of which method to use depends on judgments about what constraints should be placed on individual preferences and what factors should be considered in aggregating preferences across people.

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.

Prophylactic mastectomy or screening in women suspected to have the BRCA1/2 mutation: a prospective pilot study of women's treatment choices and medical and decision-analytic recommendations

BACKGROUND

Women suspected to have the BRCA1/2 mutation may choose between two management options: breast cancer screening and prophylactic mastectomy (PM).

OBJECTIVES

To compare women's treatment choices with medical and decision-analytic recommendations and to explore variables related to the women's choices.

METHODS

After provision of information, individual time-tradeoff values for the health outcome "living after PM" were assessed and incorporated into a decision-analytic model, which compared the management options PM and screening with respect to their effects on quality-adjusted life expectancy.

RESULTS

Of the 54 women suspected to have the mutation, 51 completed the shared-decision-making procedure. Quality-adjusted life expectancy after PM management was longer for 67% of proven carriers and for 58% of women awaiting the DNA-test result. Twelve proven carriers made definitive treatment choices: eight (67%) chose PM and four (33%) chose screening. All carriers' treatment choices agreed with the normative decision-analytic recommendations. Four (33%) disagreed with the medical recommendations. Of the 36 women awaiting DNA-test results, 32 made hypothetical treatment choices. The agreement between these hypothetical treatment choices and the decision-analytic recommendations was good (78%). Combining data from all 48 women, being married (OR = 14.00, p = 0.006), having children (OR = 4.71, p = 0.02), low desire to participate (OR = 0.14, p = 0.004), high decisional stress (OR = 5.22, p = 0.01), a lower estimate of the "probability of cure for screen-detected breast cancer" (OR = 0.13, p = 0.004), and higher time-tradeoff values for PM (OR = 182, p < 0.0001) made a choice for PM more likely.

CONCLUSIONS

The complete agreement between the decision-analytic recommendations and the carriers' choices suggests that women act in accordance with normative decision theory. The disagreement between the carriers' choices and the medical recommendations suggests that women's choices and physicians' recommendations were guided by different arguments. The strong association between time-tradeoff value and treatment choice suggests that the time-tradeoff is a valid method to assess preferences.

Probability Weighting and Utility Curvature in QALY-Based Decision Making

Quality-Adjusted Life-Years (QALYs) are currently the most important utility model in medical decision making. QALYs are calculated by adjusting years of life for the utility of the health state in which these years are spent. For normative reasons the standard gamble is the preferred method to measure health state utilities, but concern exists about its descriptive properties. Recent theoretical work has suggested that probability weighting can explain anomalies in standard gamble measurement. This paper shows that applying probability weighting in standard gamble measurement increases the consistency of QALYs with individual preferences. The consistency of QALYs with individual preferences is not significantly increased further if utility curvature is also taken into account. Copyright 1999 Academic Press.

Quality-Adjusted Life Years (QALY) Utility Models under Expected Utility and Rank Dependent Utility Assumptions

Quality-adjusted life years (QALY) utility models are multiattribute utility models of survival duration and health quality. This paper formulates six classes of QALY utility models and axiomatizes these models under expected utility (EU) and rank-dependent utility (RDU) assumptions. The QALY models investigated in this paper include the standard linear QALY model, the power and exponential multiplicative models, and the general multiplicative model. Emphasis is placed on a preference assumption, the zero condition, that greatly simplifies the axiomatizations under EU and RDU assumptions. The RDU axiomatizations of QALY models are generally similar to their EU counterparts, but in some cases, they require modification because linearity in probability is no longer assumed, and rank dependence introduces asymmetries between the domains of better-than-death health states and worse-than-death health states. Copyright 1999 Academic Press.

Valuing outcomes in health care: a comparison of willingness to pay and quality-adjusted life-years

Quality-adjusted life-years (QALYs) and willingness to pay (WTP) are two preference-based measures of health-related outcomes. In this article, we compare these two measures in eliciting individuals' preferences for health outcomes associated with shingles. To collect the necessary preference data, we administered computer-interactive interviews to a sample of 65- to 70-year-olds. We found no significant correlation between QALYs and WTP across individuals. We discuss our findings and argue that our results raise questions about whether QALYs and WTP are equivalent preference-based measures of health outcomes.

Sequence effects, health profiles, and the QALY model: in search of realistic modeling

The authors conducted an experiment to determine whether the sequence of presentation of states in a health profile would affect the valuations assigned to them. The empirical task was part of a large standardized experiment involving 104 students. Thirteen health states were valued using two variations of the time-tradeoff method. At the group level, a small but distinct overall effect of the sequence of the tradeoffs was detected after accounting for discounting effects. The respondents were not preference-indifferent concerning the sequence of health states presented. Detailed analysis at the individual level indicated that the overall sequence effect was attributable to two groups of respondents who were sensitive to the sequence of events. One small group, referred to as "best-things-first" respondents, preferred the best years first; the other group, classified as "happy-end" respondents, preferred the reverse sequence. The majority of the respondents, however, were indifferent to the sequence. These results suggest that 1) in valuation experiments involving the time-tradeoff method and 2) in applying valuation results to the evaluation of real-life health consequences, a varying lifetime health profile may not be regarded as simply a chain of independent separately valued and discounted QALY periods. Even elementary valuation tasks cannot safely assume ignorance of prognosis, as the additive utility independence assumption of the QALY model does not hold. The sequence effect at least supplements the conventional general time-preference concept, and specific strategies are suggested to disentangle quantitatively the sequence effect and the time-preference effect.

Subjective health estimations (SHE) in patients with advanced breast cancer: an adapted utility concept for clinical trials

We wished to develop and validate a simple linear analogue self-assessment (LASA) scale to assess utility values in multicentre, multicultural breast cancer trials. We compared two variants of a LASA scale (score range 0-100) with different anchoring points [perfect health to worst possible health (subjective health estimation, SHE) and perfect health to death (SHED)] in 84 patients with advanced breast cancer. Feasibility was explored in the first 48 patients interviewed. Values from the LASA scales were compared with each other and with a time trade off (TTO) interview. Scores from the two LASA scales were highly correlated (r=0.8, P < 0.0001, Spearman). The relationship between TTO interview and SHE was confirmed with tests for trend across ordered groups (linear-trend test P < 0.001). Most patients preferred SHE to SHED. SHE scores (in which high scores indicate high-health-state values) were significantly different by type of treatment, time from diagnosis and age. Thus, significantly different mean SHE scores were obtained from patients receiving no treatment or hormone therapy, mild and intensive chemotherapy (ANOVA P=0.03) and from patients with diagnosis 2 years, 2-5 years, 5-10 years and more than 10 years before interview (ANOVA P=0.02). Older patients (> 56 years) had a lower mean on the SHE scale (53 vs 61; ANOVA P=0.04). We found that the two versions of the LASA scale were equivalent for clinical purposes. SHE appeared to provide a feasible, patient-preferred and valid alternative to lengthy TTO interviews in assessing the value patients attach to their present state of health in large-scale cancer clinical trials.

Incorporating risk attitude into Markov-process decision models: importance for individual decision making

Most decision models published in the medical literature take a risk-neutral perspective. Under risk neutrality, the utility of a gamble is equivalent to its expected value and the marginal utility of living a given unit of time is the same regardless of when it occurs. Most patients, however, are not risk-neutral. Not only does risk aversion affect decision analyses when tradeoffs between short- and long-term survival are involved, it also affects the interpretation of time-tradeoff measures of health-state utility. The proportional time tradeoff under- or overestimates the disutility of an inferior health state, depending on whether the patient is risk-seeking or risk-averse (it is unbiased if the patient is risk-neutral). The authors review how risk attitude with respect to gambles for survival duration can be incorporated into decision models using the framework of risk-adjusted quality-adjusted life years (RA-QALYs). They present a simple extension of this framework that allows RA-QALYs to be calculated for Markov-process decision models. Using a previously published Markov-process model of surgical vs expectant treatment for benign prostatic hypertrophy (BPH), they show how attitude towards risk affects the expected number of QALYs calculated by the model. In this model, under risk neutrality, surgery was the preferred option. Under mild risk aversion, expectant treatment was the preferred option. Risk attitude is an important aspect of preferences that should be incorporated into decision models where one treatment option has upfront risks of morbidity or mortality.

Economic foundations of cost-effectiveness analysis

To address controversies in the applications of cost-effectiveness analysis, we investigate the principles underlying the technique and discuss the implications for the evaluation of medical interventions. Using a standard von Neumann-Morgenstern utility framework, we show how a cost-effectiveness criterion can be derived to guide resource allocation decisions, and how it varies with age, gender, income level, and risk aversion. Although cost-effectiveness analysis can be a useful and powerful tool for resource allocation decisions, a uniform cost-effectiveness criterion that is applied to a heterogeneous population level is unlikely to yield Pareto-optimal resource allocations.

Automated computer interviews to elicit utilities: potential applications in the treatment of deep venous thrombosis

OBJECTIVE

To assess the practicality of an automated computer interview as a method to assess preferences for use in decision making. To assess preferences for outcomes of deep vein thrombosis (DVT) and its treatment.

STUDY DESIGN

A multimedia program was developed to train subjects in the use of different preference assessment methods, presented descriptions of mild post-thrombotic syndrome (PTS), severe PTS and stroke and elicited subject preferences for these health states. This instrument was used to measure preferences in 30 community volunteers and 30 internal medicine physicians. We then assessed the validity of subject responses and calculated the number of quality-adjusted life years (QALYs) for each individual for each alternative.

RESULTS

All subjects completed the computerized survey instrument without assistance. Subjects generally responded positively to the program, with volunteers and physicians reporting similar preferences. Approximately 26.5% of volunteers and physicians had preferences that would be consistent with the use of thrombolysis. Individualization of therapy would lead to the most QALYs.

CONCLUSIONS

Utilization of computerized survey instruments to elicit patient preferences appears to be a practical and valid approach to individualize therapy. Application of this method suggests that there may be many patients with DVT for whom treatment with a thrombolytic drug would be optimal.

The validity of QALYs: an experimental test of constant proportional tradeoff and utility independence

Pliskin, Shepard, and Weinstein identified three preference conditions that ensure that quality-adjusted life years (QALYs) represent preferences over gambles over chronic health profiles. This paper presents an experimental test of the descriptive validity of two of these preference assumptions: utility independence and constant proportional tradeoff. Eighty students at the Stockholm School of Economics and 92 students at Erasmus University Rotterdam participated in the experiment. The results of the experiment support the descriptive validity of constant proportional tradeoff: both within groups and between groups constant proportional tradeoff could not be rejected. The results are less supportive of the descriptive validity of utility independence. Within-groups utility independence was rejected. Between-groups utility independence could not be rejected, but this may have been due to a lack of statistical power. Analysis of the individual responses revealed that without adjustment for imprecision of preference, 39 respondents (22.8%) satisfied constant proportional tradeoff. Twenty-three respondents (13.4%) satisfied utility independence without adjustment for imprecision of preference. However, because of the relative unfamiliarity of the respondents with both the health states to be evaluated and the methods of health-state-utility measurement, it is likely that the respondents' preferences were imprecise. Adjusted for imprecision of preference, the upper estimates of the proportions of respondents who satisfied constant proportional tradeoff and utility independence, respectively, were 90.1% (155 respondents) and 75.6% (130 respondents). Pliskin et al. further derived that if an individual's preferences satisfy both constant proportional tradeoff and utility independence, then these preferences can be represented by a more general, risk-adjusted QALY model. Without adjustment for imprecision of preference, ten respondents (5.8%) satisfied both constant proportional tradeoff and utility independence. Adjusted for imprecision of preference, the upper estimate of the proportion of respondents who satisfied both constant proportional tradeoff and utility independence was 68.6% (118 respondents). The results of this study indicate that constant proportional tradeoff holds approximately. The evidence is much weaker for utility independence, however. This has important implications for the use of QALY-type measures in medical decision making.