The "utility" of the Time Trade-Off method in cancer patients: feasibility and proportional Trade-Off

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.

Estimating loss in quality of life associated with asthma-related crisis events (ESQUARE): a cohort, observational study

Background

Evidence of quality of life implications of asthma attacks are limited, particularly when measured on a utility scale, which enables calculating Quality-Adjusted Life-Years (QALYs) and comparisons with other health conditions and services. Therefore, this study sought to estimate the utility loss associated with an asthma-related crisis event (accident and emergency (A&E) attendance or hospital admission).

Methods

Participants were recruited in a cohort study from A&E and hospital admissions at three UK hospitals. They completed the EuroQol-5 Dimensions 5-Level (EQ-5D-5 L), Asthma Quality of Life Questionnaire (AQLQ), Time trade-off (TTO), and peak flow and symptom diary over 8 weeks, where three different methods (EQ-5D-5 L, AQLQ, and TTO), were used to estimate utilities. The mean difference between two time points were estimated using the Wilcoxon signed rank test.

Results

From baseline to week 8, mean increases (95% CI) were estimated to be 0.086 (0.019–0.153), 0.154 (0.112–0.196) and 0.132 (0.063–0.201) for EQ-5D-5 L, AQL-5D (preference-based measure derived from AQLQ), and TTO respectively over 8 weeks (p < 0.01).

Conclusion

Asthma crisis events are estimated to be associated with a mean utility loss of between 0.086 and 0.132. The utility decrement can be used to assign values to asthma-related crisis events, which can enhance economic evaluations.

Trial registration

NCT02771678. Registered 13 May 2016.

Electronic supplementary material

The online version of this article (10.1186/s12955-019-1138-5) contains supplementary material, which is available to authorized users.

Overview, Update, and Lessons Learned From the International EQ-5D-5L Valuation Work: Version 2 of the EQ-5D-5L Valuation Protocol

A standardized 5-level EuroQol 5-dimensional questionnaire (EQ-5D-5L) valuation protocol was first used in national studies in the period 2012 to 2013. A set of problems encountered in this initial wave of valuation studies led to the subsequent refinement of the valuation protocol. To clarify lessons learned and how the protocol was updated when moving from version 1.0 to the current version 2.1 and 2.0, this article will (1) present the challenges faced in EQ-5D-5L valuation since 2012 and how these were resolved and (2) describe in depth a set of new challenges that have become central in currently ongoing research on how EQ-5D-5L health states should be valued and modeled.

The time horizon matters: results of an exploratory study varying the timeframe in time trade-off and standard gamble utility elicitation

INTRODUCTION

The purpose of this study was to examine whether the time horizon of time trade-off (TTO) and standard gamble (SG) utility assessment influences utility scores and discrimination between health states.

METHODS

In two phases, UK general population participants rated three osteoarthritis health states in TTO and SG procedures with two time horizons: (1) 10-year and (2) a time horizon derived from self-reported additional life expectancy (ALE). The two time horizons were compared in terms of mean utilities and discrimination among health states.

RESULTS

In Phase 1, the 10-year tasks were completed by 80 participants, 35 of whom also completed utility assessment with the ALE. In Phase 2, all 101 participants completed procedures with both time horizons. Utility scores tended to be lower with the ALE than the 10-year, a difference that was statistically significant for two health states with SG in Phase 1 (P < 0.05), two health states with TTO in Phase 2 (P < 0.01), and one health state with SG in Phase 2 (P < 0.001). In Phase 1, rates of discrimination between mild and moderate osteoarthritis health states were significantly higher with the ALE than the 10-year (TTO: P = 0.03; SG: P = 0.001). This pattern of discrimination was similar in Phase 2.

DISCUSSION

Results suggest that the time horizon could influence utility scores and discrimination among health states. When designing utility evaluations, researchers should carefully consider the time horizon so that the value of health states is accurately represented in cost-utility models.

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.

Valuation of depression co-occurring with a somatic condition: feasibility of the time trade-off task

BACKGROUND

Health state valuations obtained from the general population are used for cost-utility analyses of health-care interventions. Currently, most studies have focused on valuations of somatic conditions, to a much lesser extent of mental states, that is, depression and even less on valuations of depression co-occurring with somatic conditions.

OBJECTIVE

We tested the feasibility of the time trade-off (TTO) task to elicit valuations for depression solitary or co-occurring with a somatic condition. Moreover, we explored person- and state-related factors that may affect valuations.

DESIGN

During semi-structured interviews, 10 individuals (five women, mean age: 36 years) used a TTO task to value vignettes describing mild and severe depression; and mild depression co-occurring with moderate and severe states of cancer, diabetes or heart disease. During valuations, participants were thinking aloud. Feasibility criteria were successful completion and difficulty/concentration (1-10); logical consistency of values; and comprehension of the TTO, based on qualitative analysis of think aloud data. Factors influencing valuations were generated from think aloud data.

RESULTS

Participants reported satisfactory levels of difficulty (mean: 1.9) and concentration (mean: 8.3) and assigned consistent values. Qualitative analysis revealed difficulties with imagining: living with depression for lifetime (n = 4); reaching the age of 80 (n = 6); and living with a somatic condition and mentally healthy (n = 6). Person- and state-related factors, for example perceived susceptibility to depression (n = 4), appeared to affect valuations.

CONCLUSION

Quantitative findings supported feasibility of the valuation protocol, yet qualitative findings indicated that certain task aspects should be readdressed. Factors influencing valuations can be explored to better understand valuations.

Health state utilities associated with attributes of treatments for hepatitis C

BACKGROUND

Cost-utility analyses are frequently conducted to compare treatments for hepatitis C, which are often associated with complex regimens and serious adverse events. Thus, the purpose of this study was to estimate the utility associated with treatment administration and adverse events of hepatitis C treatments.

DESIGN

Health states were drafted based on literature review and clinician interviews. General population participants in the UK valued the health states in time trade-off (TTO) interviews with 10- and 1-year time horizons. The 14 health states described hepatitis C with variations in treatment regimen and adverse events.

RESULTS

A total of 182 participants completed interviews (50% female; mean age = 39.3 years). Utilities for health states describing treatment regimens without injections ranged from 0.80 (1 tablet) to 0.79 (7 tablets). Utilities for health states describing oral plus injectable regimens were 0.77 (7 tablets), 0.75 (12 tablets), and 0.71 (18 tablets). Addition of a weekly injection had a disutility of -0.02. A requirement to take medication with fatty food had a disutility of -0.04. Adverse events were associated with substantial disutilities: mild anemia, -0.12; severe anemia, -0.32; flu-like symptoms, -0.21; mild rash, -0.13; severe rash, -0.48; depression, -0.47. One-year TTO scores were similar to these 10-year values.

CONCLUSIONS

Adverse events and greater treatment regimen complexity were associated with lower utility scores, suggesting a perceived decrease in quality of life beyond the impact of hepatitis C. The resulting utilities may be used in models estimating and comparing the value of treatments for hepatitis C.

Impact of caregiver and parenting status on time trade-off and standard gamble utility scores for health state descriptions

Background

The purpose of this study was to examine the effect of caregiver status on time trade-off (TTO) and standard gamble (SG) health state utility scores. Respondents were categorized as caregivers if they reported that either children or adults depended on them for care.

Methods

This study was a secondary analysis of data from three studies in which general population samples rated health state descriptions. Study 1: UK; four osteoarthritis health states. Study 2: UK; three adult ADHD health states. Study 3: US; 16 schizophrenia health states. All three studies included time trade-off assessment. Study 1 also included standard gamble. Descriptive statistics were calculated to examine willingness to trade in TTO or gamble in SG. Utilities for caregivers and non-caregivers were compared using t-tests and ANCOVA models.

Results

There were 364 respondents including 106 caregivers (n = 30, 47, and 29 in Studies 1, 2, and 3) and 258 non-caregivers. Most caregivers were parents of dependent children (78.3%). Compared to non-caregivers, caregivers had more responses at the ceiling (i.e., utility = 0.95), indicating less willingness to trade time or gamble. All utilities were higher for caregivers than non-caregivers (mean utility difference between groups: 0.07 to 0.16 in Study 1 TTO; 0.03 to 0.17 in Study 1 SG; 0.06 to 0.10 in Study 2 TTO; 0.11 to 0.22 in Study 3 TTO). These differences were statistically significant for at least two health states in each study (p < 0.05). Results of sensitivity analyses with two caregiver subgroups (parents of dependent children and parents of any child regardless of whether the child was still dependent) followed the same pattern as results of the primary analysis. The parent subgroups were generally less willing to trade time or gamble (i.e., resulting in higher utility scores) than comparison groups of non-parents.

Conclusions

Results indicate that caregiver status, including being a parent, influences responses in time trade-off health state valuation. Caregivers (i.e., predominantly parents) were less willing than non-caregivers to trade time, resulting in higher utility scores. This pattern was consistent across multiple health states in three studies. Standard gamble results followed similar patterns, but with less consistent differences between groups. It may be useful to consider parenting/caregiving status when collecting, interpreting, or using utility data because this demographic variable could influence results.

Qualitative and Quantitative Analysis of Interviewer Help Answering the Time Tradeoff

OBJECTIVES

The time tradeoff (TTO) is an important method to directly obtain health utilities. Challenges of the TTO are, among others, "nontraders" and illogical answers. In TTO interviews, these challenges are resolved by the interviewer. In web-based TTOs, training procedures and logical checks are used based on the views of the researchers. As web-based TTOs will be used more often in the future, we investigated how respondents arrive at their ratings to determine the help they require.

METHODS

In 2 earlier studies performed by this research group, respondents valued 6 EQ-5D states on a TTO. Respondents were asked to think out loud, and all interviews were audiotaped. A random selection of these interviews were transcribed and double-coded by two independent raters, using a priori and inductive coding until saturation was reached. Based on the retrieved mistakes and comments, a list of frequently asked questions (FAQ) was developed.

RESULTS

In total, 91 interviews were coded. In all, 85% made at least 1 mistake, 41% made a misreading/miscalculation, 70% misunderstood the tradeoff, 27% misunderstood the EQ-5D dimensions, 29% misunderstood the scenario, 45% made a comment about the TTO, and 43% expressed frustration. More misunderstandings were reported in the Peeters study, which was performed in a realistic setting, whereas the van Osch study was conducted in a more ideal setting. Misunderstandings of the scenario were mosly reported by patients.

CONCLUSIONS

Almost all respondents need interviewer help. This may have implications for the validity of interviewer-based TTO elicitations when social acceptability bias is an issue or with explicit hypothesis and the interviewer is not blinded. The FAQ list can be used to standardize interviewer help or as a help function in a web-based TTO.

Health state utilities for skeletal-related events secondary to bone metastases

INTRODUCTION

Patients with bone metastases often experience skeletal-related events (SREs). Although cost-utility models are used to examine treatments for metastatic cancer, limited information is available on utilities of SREs. The purpose of this study was to estimate the disutility of four SREs: spinal cord compression, pathological fracture, radiation to bone, and surgery performed to stabilize a bone.

METHODS

General population participants from the UK and Canada completed time trade-off (TTO) interviews to assess the utility of health states drafted based on literature review, clinician interviews, and patient interviews. Respondents first rated a health state describing cancer with bone metastases. Then, the SREs were added to this health state.

RESULTS

Interviews were completed with 187 participants (50.8 % male, 80.2 % white). Cancer with bone metastases without an SRE had a mean utility of 0.47 (SD = 0.43) on a standard utility scale (1 = full health, 0 = death). Of the SREs, spinal cord compression was associated with the greatest disutility (i.e., the utility decrease): -0.32 with paralysis and -0.22 without paralysis. Surgery had a disutility of -0.07. Leg, arm, and rib fractures had disutilities of -0.06, -0.04, and -0.03. Two weeks of daily radiation treatment had a disutility of -0.06, while two radiation appointments had the smallest impact on utility (-0.02).

CONCLUSION

All SREs were associated with statistically significant utility decreases, suggesting a perceived impact on quality of life beyond the impact of cancer with bone metastases. The resulting disutilities may be used in cost-utility models examining treatments to prevent SREs secondary to bone metastases.

Use of forecasted assessment of quality of life to validate time-trade-off utilities and a prostate cancer screening decision-analytic model

PURPOSE

To determine whether the forecasted assessment of how someone would feel in a future health state can be predictive of utilities (e.g. as elicited by the time-trade-off method) and also predictive of optimal decisions as determined by a decision-analytic model.

METHODS

We elicited time-trade-off utilities for prostate cancer treatment outcomes from 168 men. We also elicited forecasted assessments, that is, an informal, non-quantitative, descriptive evaluation, of impotence and incontinence from these men. We used multivariate regression analysis to explore the relationship between forecasted assessment and reluctance to trade length for improved quality of life, that is, the unwillingness to trade length of life for improved quality of life in the time-trade-off utility assessment and the relationship between the forecasted assessments and the optimal decision of whether to undergo screening for prostate cancer as determined from a previously published decision-analytic model.

RESULTS

Importance of sexual function was strongly related to impotence utilities (P < 0.05). Based on the multivariate analysis, significant predictors for the utility of severe incontinence were family income, family history of prostate cancer, work status and attitude towards needing to wear an incontinence pad. However, no variables were statistically significant predictors for the utility of complete impotence. The importance of sexual functioning was a significant predictor of the optimal decision.

CONCLUSION

Anticipated difficulty adjusting to adverse health effects were highly related to preferences and could be used as a proxy measure of utility. Similarly, the importance of sexual functioning, a future preference, was highly related to the optimal decision, which validates our previously published decision-analytic model.

Time trade-off: one methodology, different methods

There is no scientific consensus on the optimal specification of the time trade-off (TTO) task. As a consequence, studies using TTO to value health states may share the core element of trading length of life for quality of life, but can differ considerably on many other elements. While this pluriformity in specifications advances the understanding of TTO from a methodological point of view, it also results in incomparable health state values. Health state values are applied in health technology assessments, and in that context comparability of information is desired. In this article, we discuss several alternative specifications of TTO presented in the literature. The defining elements of these specifications are identified as being either methodological, procedural or analytical in nature. Where possible, it is indicated how these elements affect health state values (i.e., upward or downward). Finally, a checklist for TTO studies is presented, which incorporates a list of choices to be made by researchers who wish to perform a TTO task. Such a checklist enables other researchers to align methodologies in order to enhance the comparability of health state values.

The impact of patients' subjective life expectancy on time tradeoff valuations

BACKGROUND

Quality-adjusted life-year (QALY) calculations in economic evaluations are typically based on general public or patient health state valuations elicited with the time tradeoff method (TTO). Such health state valuations elicited among the general public have been shown to be affected by respondents' subjective life expectancy (SLE). This suggests that TTO exercises based on time frames other than SLE may lead to biased estimates. It has not yet been investigated whether SLE also affects patient valuations.

OBJECTIVE

To empirically investigate whether patients' SLE affects TTO valuations of their current health state.

METHODS

Patients with different severities of diabetic retinopathy were asked in a telephone interview to value their own health status using TTO. The TTO time frame (t) presented was based on age- and sex-dependent actuarial life expectancy. Patients were then asked to state their SLE. Simple and multiple regression techniques were used to assess the effect of the patients' SLE on their TTO responses.

RESULTS

In total, 145 patients completed the telephone interview. Patients' TTO values were significantly influenced by their SLE. The TTO value decreased linearly with every additional year of difference between t and the patients' SLE; that is, patients were more willing to give up years the shorter their SLE compared with t.

CONCLUSION

Patients' SLE influenced their TTO valuations, suggesting that respondents' SLE may be the most appropriate time frame to use in TTO exercises in patients. The use of other time periods may bias the TTO valuations, as the respondents may experience the presented time frame as a gain or a loss. The effect seems to be larger in patient valuations than in general public valuations.

The way that you do it? An elaborate test of procedural invariance of TTO, using a choice-based design

The time tradeoff (TTO) method is often used to derive Quality-Adjusted Life Year health state valuations. An important problem with this method is that results have been found to be responsive to the procedure used to elicit preferences. In particular, fixing the duration in the health state to be valued and inferring the duration in full health that renders an individual indifferent, causes valuations to be higher than when the duration in full health is fixed and the duration in the health state to be valued is elicited. This paper presents a new test of procedural invariance for a broad range of time horizons, while using a choice-based design and adjusting for discounting. As one of the known problems with the conventional procedure is the violation of constant proportional tradeoffs (CPTO), we also investigate CPTO for the alternative TTO procedure. Our findings concerning procedural invariance are rather supportive for the TTO procedure. We find no violations of procedural invariance except for the shortest gauge duration. The results for CPTO are more troublesome: TTO scores depend on gauge duration, reinforcing the evidence reported when using the conventional procedure.

Cost-effectiveness analysis of a randomized study comparing radiosurgery with radiosurgery and whole brain radiation therapy in patients with 1 to 3 brain metastases

BACKGROUND

In this study, we compare 2 treatment options and determine cost-effectiveness and cost-utility.

METHODS

We carried out a decision analysis populated with data from patients with brain metastasis in a concurrent trial randomized to either stereotactic radiosurgery (SRS) and observation or SRS and whole brain radiation therapy. Outcomes included actual life years saved (LYS), quality-adjusted life years (QALYs), and incremental cost-effectiveness ratio (ICER). Costs used were from the healthcare perspective and utilities were captured through a time-trade-off method, using 10-year, 5-year, and 1-year time horizons. One-way sensitivity analyses were carried out to determine robustness of the decision analysis model.

RESULTS

Compared with SRS and whole brain radiation therapy, SRS and observation not only had a higher average cost ($74,000 vs $119,000, respectively) but also a higher average effectiveness (0.60 LYS vs 1.64 LYS, respectively) with an ICER of $44,231/LYS or $41,783/QALY (with utilities captured using a 10-year horizon). Slightly higher ICER estimates were achieved with utilities captured using the other time horizons ($43,280/QALY and $44,064/QALY, respectively). Sensitivity analysis showed that the following variables had the highest impact on the ICER: probability of no recurrence in recursive-partitioning analysis class 2 after SRS and observation; probability of being alive after SRS and observation in recursive-partitioning analysis class 2 and being treated for recurrence.

CONCLUSIONS

Compared with other interventions in the $50,000 to $100,000/QALY cost-effectiveness range, the application of SRS and observation, with subsequent neurosurgical management of recurrences, is shown to be a reasonable treatment modality for brain metastases.

A test of independence of discounting from quality of life

The quality-adjusted life-years (QALY) model assumes quality and quantity of life can be multiplied into a single index and requires quality and quantity to be mutually independent, which need not hold empirically. This paper proposes a new test for measuring independence of utility of life duration from quality of life in a riskless setting. We use a large representative sample of Dutch citizens and include two health states generally considered better than dead (BTD) and one health state considered worse than dead (WTD). Independence cannot be rejected when comparing the BTD health states, but is rejected when comparing the BTD states with the WTD state. In particular, utility of life duration becomes more concave for the WTD state. This may suggest that independence holds only for BTD health states. This has implications for the QALY model and would require using sign-dependent utility of life duration functions.

Using QALYs in cancer: a review of the methodological limitations

The objective of this paper is to examine how well the QALY captures the health gains generated by cancer treatments, with particular focus on the methods for constructing QALYs preferred by the UK National Institute for Health and Clinical Excellence (NICE). Data were obtained using a keyword search of the MEDLINE database and a hand search of articles written by leading researchers in the subject area (with follow up of the references in these articles). Key arguments were discussed and developed at an oncology workshop in September 2009 at the Office of Health Economics. Three key issues emerged. First, the EQ-5D, NICE's preferred measure of health-related quality of life (QOL) in adults, has been found to be relatively insensitive to changes in health status of cancer patients. Second, the time trade-off, NICE's preferred technique for estimating the values of health states, involves making assumptions that are likely to be violated in end-of-life scenarios. Third, the practice of using valuations of members of the general population, as recommended by NICE, is problematic because such individuals typically display a misunderstanding of what it is really like for patients to live with cancer. Because of the way in which it is constructed, the QALY shows important limitations in terms of its ability to accurately capture the value of the health gains deemed important by cancer patients. A research agenda for addressing these limitations is proposed.

Effect of adaptive abilities on utilities, direct or mediated by mental health?

Background

In cost-utility analyses gain in health can be measured using health state utilities. Health state utilities can be elicited from members of the public or from patients. Utilities given by patients tend to be higher than utilities given by members of the public. This difference is often suggested to be explained by adaptation, but this has not yet been investigated in patients. Here, we investigate if, besides health related quality of life (HRQL), persons' ability to adapt can explain health state utilities. Both the direct effect of persons' adaptive abilities on health state utilities and the indirect effect, where HRQL mediates the effect of ability to adapt, are examined.

Methods

In total 125 patients with Rheumatoid Arthritis were interviewed. Participants gave valuations of their own health on a visual analogue scale (VAS) and time trade-off (TTO). To estimate persons' ability to adapt, patients filled in questionnaires measuring Self-esteem, Mastery, and Optimism. Finally they completed the SF-36 measuring HRQL. Regression analyses were used to investigate the direct and mediated effect of ability to adapt on health state utilities.

Results

Persons' ability to adapt did not add considerably to the explanation of health state utilities above HRQL. In the TTO no additional variance was explained by adaptive abilities (Δ R² = .00, β = .02), in the VAS a minor proportion of the variance was explained by adaptive abilities (Δ R² = .05, β = .33). The effect of adaptation on health state utilities seems to be mediated by the mental health domain of quality of life.

Conclusions

Patients with stronger adaptive abilities, based on their optimism, mastery and self-esteem, may more easily enhance their mental health after being diagnosed with a chronic illness, which leads to higher health state utilities.

On the (not so) constant proportional trade-off in TTO

Purpose

The linear and power QALY models require that people in Time Trade-off (TTO) exercises sacrifice the same proportion of lifetime to obtain a health improvement, irrespective of the absolute amount. However, evidence on these constant proportional trade-offs (CPTOs) is mixed, indicating that these versions of the QALY model do not represent preferences. Still, it may be the case that a more general version of the QALY model represents preferences. This version has the property that people want to sacrifice the same proportion of utilities of lifetime for a health improvement, irrespective of the amount of this lifetime.

Methods

We use a new method to correct TTO scores for utility of life duration and test whether decision makers trade off utility of duration and quality at the same rate irrespective of duration.

Results

We find a robust violation of CPTO for both uncorrected and corrected TTO scores. Remarkably, we find higher values for longer durations, contrary to most previous studies. This represents the only study correcting for utility of life duration to find such a violation.

Conclusions

It seems that the trade-off of life years is indeed not so constantly proportional and, therefore, that health state valuations depend on durations.

A comparison of preferences for two GLP-1 products--liraglutide and exenatide--for the treatment of type 2 diabetes

OBJECTIVE

To use time trade-off (TTO) to compare patient preferences for profiles of two glucagon-like peptide (GLP-1) products for the treatment of type 2 diabetes (liraglutide and exenatide) that vary on four key attributes - efficacy (as measured by hemoglobin A(1C)), incidence of nausea, incidence of hypoglycemia, and dosing frequency (QD vs. BID) - and measure the contribution of those attributes to preferences.

METHODS

A total of 382 people with T2DM were recruited to participate in an internet-based survey consisting of a series of health-related questions, a conjoint exercise and a set of time trade-off items. In the conjoint exercise, respondents were presented with eight pairs of hypothetical GLP-1 profiles, and completed a time-tradeoff exercise for each pair.

RESULTS

The product profile representing liraglutide was preferred by 96% of respondents and resulted in significantly higher health utilities (0.038) than the product profile representing exenatide (0.978 vs. 0.94, p < 0.05). Estimated preference scores from the conjoint analysis revealed that efficacy measured by hemoglobin A(1C) is the most important attribute, followed by nausea, hypoglycemia, and dosing schedule.

LIMITATIONS

On-line participants may not represent 'typical' type 2 diabetes patients, and brief product profiles represented results from clinical trials, not clinical practice

CONCLUSION

Based on the four attributes presented, patients prefer liraglutide over exenatide. Preference is based on superior efficacy and less nausea more than less hypoglycemia and once-daily dosing.

The duration effect: a link between TTO and VAS values

The value of a health state may depend on how long an individual has had to endure the health state (i.e. hedonic load). In this paper, we test the constant proportionality (CP) assumption and determine the sign of relationship between duration and health state value for 42 health states using the nationally representative data from the United Kingdom Measurement and Valuation of Health study. The results reject the CP assumption and suggest that the relationship is negative for optimal health (i.e. fair innings argument) and that the relationship is positive for poorer health states (i.e. adaptation). We find no evidence of the maximum endurable time hypothesis using these data. This evidence on the duration effect has important implications for outcomes research and the economic evaluation of interventions.

Can we fix it? Yes we can! But what? A new test of procedural invariance in TTO-measurement

The TTO-method is often used to value health states, but it is susceptible to several biases and methodological difficulties. One of these is a violation of procedural invariance, which means that the way a TTO-question is framed, i.e. either by fixing the period in imperfect health or that in perfect health, can have a substantial effect on the elicited value of a health state. There are four important sources of discrepancy of the two procedures: loss aversion, maximum endurable time, scale compatibility and discounting. In this article, we present the results of a new test of procedural invariance in which we avoided or corrected for two of these sources (discounting and maximum endurable time). Our results indicate that while correcting for discounting does diminish the difference between the two TTO-procedures, a large and significant violation of procedural invariance remains. Loss aversion is probably the main determinant of the remainder of this difference.

Why people refuse to make tradeoffs in person tradeoff elicitations: a matter of perspective?

OBJECTIVE

Person tradeoff (PTO) elicitations assess people's values for health states by asking them to compare the value of treatment programs. For example, people might be asked how many patients need to be cured of health condition X to equal the benefit of curing 100 people of condition Y. However, when faced with PTO elicitations, people frequently refuse to make quantifiable tradeoffs, exhibiting 2 kinds of refusals: 1) They say that 2 treatment programs have equal value, that curing 100 of X is just as good as curing 100 of Y, even if X is a less serious condition than Y, or 2) they say that the 2 programs are incomparable, that millions of people need to be cured of X to be as good as curing 100 of Y. The authors explore whether people would be more willing to make tradeoffs if the focus was changed from trading off groups of patients to choosing the best decision or evaluating treatment benefits.

DESIGN

. Two randomized trials used diverse samples (N=2400) via the Internet to test for the effect of perspective on refusal rates. The authors predicted that perspectives that removed people from decision-making roles would increase their willingness make tradeoffs.

RESULTS

Contrary to expectations, refusal rates increased when people were removed from decision-making roles. In fact, the more pressure put on people to make a decision, the less likely they were to refuse to make tradeoffs.

CONCLUSION

To reduce PTO refusals, it is best to adopt a decision-maker perspective.

Cost-utility analysis when not everyone wants the treatment: modeling split-choice bias

Not all clinically eligible patients will necessarily accept a new treatment. Cost-utility analysis recognizes this by multiplying the mean incremental expected utility (EU) by the participation rate to obtain the utility gain per head. However, the mean EU gain over all patients in a defined clinical category is traditionally used as a proxy for the mean EU gain over the subpopulation of acceptors. Even for clinically identical patients, this may lead to a biased assessment of total benefit because a patient motivated to accept the new treatment is likely to value its effects more favorably than a patient who declines. An analysis that ignores this tendency will be biased toward an underestimate of true benefits of a health technology (HT). The extent of this bias is described within a quality-adjusted life year-based utility model for a population of clinically indistinguishable patients who differ with respect to the values that they place on the possible health outcomes of an HT. The size of the bias is sensitive to the proportion of patients who accept the treatment, under both deterministic and probabilistic models of individual decision making. In all cases in which decision making is correlated with personal utility gain, the bias rises steeply as the proportion of acceptors declines.

Quality of life in age-related macular degeneration: a review of the literature

BACKGROUND

The Age-related Macular Degeneration Alliance International commissioned a review of the literature on quality of life (QoL) in macular degeneration (MD) with a view to increasing awareness of MD, reducing its impact and improving services for people with MD worldwide.

METHOD

A systematic review was conducted using electronic databases, conference proceedings and key journal hand search checks. The resulting 'White Paper' was posted on the AMD Alliance website and is reproduced here.

REVIEW

MD is a chronic, largely untreatable eye condition which leads to loss of central vision needed for tasks such as reading, watching TV, driving, recognising faces. It is the most common cause of blindness in the Western world. Shock of diagnosis, coupled with lack of information and support are a common experience. Incidence of depression is twice that found in the community-dwelling elderly, fuelled by functional decline and loss of leisure activities. Some people feel suicidal. MD threatens independence, especially when comorbidity exacerbates functional limitations. Rehabilitation, including low vision aid (LVA) provision and training, peer support and education, can improve functional and psychological outcomes but many people do not receive services likely to benefit them. Medical treatments, suitable for only a small minority of people with MD, can improve vision but most limit progress of MD, at least for a time, rather than cure. The White Paper considers difficulties associated with inappropriate use of health status measures and misinterpretation of utility values as QoL measures: evidence suggests they have poor validity in MD.

CONCLUSION

There is considerable evidence for the major damage done to QoL by MD which is underestimated by health status and utility measures. Medical treatments are limited to a small proportion of people. However, much can be done to improve QoL by early diagnosis of MD with good communication of prognosis and continuing support. Support could include provision of LVAs, peer support, education and effective help in adjusting to MD. It is vital that appropriate measures of visual function and QoL be used in building a sound evidence base for the effectiveness of rehabilitation and treatment.

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.

Quantifying trade-offs: quality of life and quality-adjusted survival in a randomised trial of chemotherapy in postmenopausal patients with lymph node-negative breast cancer

We evaluated quality of life (QL) and quality-adjusted survival in International Breast Cancer Study Group Trial IX, a randomised trial including 1669 eligible patients receiving tamoxifen for 5 years or three prior cycles of cyclophosphamide, methotrexate and 5-fluorouracil (CMF) followed by 57 months tamoxifen. During the time with CMF toxicity (Tox), without symptoms and toxicity (TWiST), and following relapse (Rel), patients scored their QL indicators and a utility indicator for subjective health estimation between ‘perfect’ and ‘worst’ health. Scores were averaged within Tox, TWiST and Rel and transformed to utilities. Mean durations for the three transition times were weighted with utilities to obtain mean quality-adjusted TWiST (Q-TWiST). Patients receiving CMF reported significantly worse scores for most QL domains at month 3, but less hot flushes. After completing chemotherapy, there were no differences by treatment groups. Benefits evaluated by Q-TWiST favoured the additional chemotherapy. CMF provided 3 more months of Q-TWiST for patients with ER-negative tumours, but CMF provided no benefit in Q-TWiST for patients with ER-positive tumours. Q-TWiST analysis based on patient ratings is feasible in large-scale cross-cultural clinical trials.

Are QALYs based on time trade-off comparable?--A systematic review of TTO methodologies

A wide range of methods is used to elicit quality-of-life weights of different health states to generate 'Quality-adjusted life years' (QALYs). The comparability between different types of health outcomes at a numerical level is the main advantage of using a 'common currency for health' such as the QALY. It has been warned that results of different methods and perspectives should not be directly compared in QALY league tables. But do we know that QALYs are comparable if they are based on the same method and perspective?The Time trade-off (TTO) consists in a hypothetical trade-off between living shorter and living healthier. We performed a literature review of the TTO methodology used to elicit quality-of-life weights for own, current health. Fifty-six journal articles, with quality-of-life weights assigned to 102 diagnostic groups were included. We found extensive differences in how the TTO question was asked. The time frame varied from 1 month to 30 years, and was not reported for one-fourth of the weights. The samples in which the quality-of-life weights were elicited were generally small with a median size of 53 respondents. Comprehensive inclusion criteria were given for half the diagnostic groups. Co-morbidity was described in less than one-tenth of the groups of respondents. For two-thirds of the quality-of-life weights, there was no discussion of the influence of other factors, such as age, sex, employment and children. The different methodological approaches did not influence the TTO weights in a predictable or clear pattern. Whether or not it is possible to standardise the TTO method and the sampling procedure, and whether or not the TTO will then give valid quality-of-life weights, remains an open question.This review of the TTO elicited on own behalf, shows that limiting cost-utility analysis to include only quality life weights from one method and one perspective is not enough to ensure that QALYs are comparable.

Colorectal Cancer Screening and Treatment: Review of Outcomes Research

BACKGROUND

Colorectal cancer is the second leading cause of cancer deaths in the United States each year. Screening is effective in reducing colorectal cancer mortality; however, compliance with screening is poor, and factors associated with its compliance are poorly understood. The outcomes of treatment of colorectal cancer (surgery, radiation therapy, and chemotherapy) may have profound effects on quality of life (QOL). Furthermore, colorectal cancer screening and treatment may be expensive, and the costs are important from a policy perspective. This review examines patient-centered outcomes research related to colorectal cancer screening and treatment and outlines the work that has been done in several areas, including patient preferences, QOL, and economic analysis.

METHODS

The literature on the health outcomes associated with colorectal cancer screening and treatment was reviewed. A MEDLINE search of English language articles published from January 1, 1990 through February 2001, was conducted and was supplemented by a review of references of obtained articles. Criteria for study inclusion were identified a priori. A standardized data abstraction form was developed. Summary statistical analyses were performed on the results.

RESULTS

Six hundred eighty-six articles were selected for review. In total, 530 articles were excluded because they either did not include patient-centered outcomes, were duplicate articles, or could not be obtained. There were 156 articles included in the analysis; 67 addressed screening, 18 examined surveillance of high-risk groups, 22 concerned treatment of local disease, 10 examined treatment of local and metastatic disease, and 19 considered treatment of metastatic disease only. One study examined end-of-life care. In 19 studies, the phase of care was unspecified.

CONCLUSIONS

Standardized, disease-specific QOL instruments should be applied in clinical trials so that the results may be compared across different types of interventions. Valid and reliable methods that accurately capture patient preferences regarding screening and treatment should be developed.

Burden of illness in cancer survivors: findings from a population-based national sample

BACKGROUND

Population trends in aging and improved cancer survival are likely to result in increased cancer prevalence in the United States, but few estimates of the burden of illness among cancer survivors are currently available. The purpose of this study was to estimate the burden of illness in cancer survivors in a national, population-based sample.

METHODS

A total of 1823 cancer survivors and 5469 age-, sex-, and educational attainment-matched control subjects were identified from the 2000 National Health Interview Survey. Multiple measures of burden, including utility, a summary measure of health, and days lost from work, were compared using two-sided tests of statistical significance for the two groups overall and for subgroups stratified by tumor site and time since diagnosis.

RESULTS

Compared with matched control subjects, cancer survivors had poorer outcomes across all burden measures (P<.01). Cancer survivors had lower utility values (0.74 versus 0.80; P<.001) and higher levels of lost productivity and were more likely to report their health as fair or poor (31.0% versus 17.9%; P<.001) than matched control subjects. Cancer survivors reported statistically significantly higher burden than did control subjects across tumor sites and across time since diagnosis (i.e., within the past year, 2-5 years, 6-10 years, and > or =11 years for the majority of measures.

CONCLUSIONS

Cancer survivors have poorer health outcomes than do similar individuals without cancer across multiple burden measures. These decrements are consistent across tumor sites and are found in patients many years following reported diagnosis. Improved measurement of long-term burden of illness will be important for future prospective research.

Are health states 'timeless'? A case study of an acute condition: post-chemotherapy nausea and vomiting

RATIONALE, AIMS AND OBJECTIVES

The objective was to test whether individuals' responses to standard gamble (SG) and visual analogue scale (VAS) questions do not depend on the time horizon of the health scenario presented.

METHODS

Face-to-face interviews were conducted in a convenience sample of 18 women aged 22-50 years with no history of breast cancer or cancer requiring chemotherapy. Data were collected from March 2000 to June 2000 at a university in the Midwest of the United States of America. Preference weights were estimated using SG top-down titration method and VAS scaled from zero (death) to one (perfect health). Subjects were asked to rate their preferences if faced with two scenarios: post-chemotherapy nausea and vomiting (PCNV) occurring for 3 days (scenario 1), and PCNV lasting for the rest of their lives (scenario 2). Three PCNV health states of varying severity were tested: complete alleviation, partial alleviation, and no alleviation.

RESULTS

Paired-t-test analysis showed statistically significantly lower preference weights (P < 0.05) when the health state was for the rest of the respondent's life vs. 3 days. Mean SG weights for scenario 1 vs. scenario 2 were: 0.968 vs. 0.927 (complete alleviation), 0.942 vs. 0.810 (partial alleviation) and 0.866 vs. 0.644 (no alleviation). Mean VAS weights for scenario 1 vs. scenario 2 were: 0.741 vs. 0.676 (complete alleviation), 0.490 vs. 0.307 (partial alleviation) and 0.276 vs. 0.136 (no alleviation).

DISCUSSION AND CONCLUSIONS

For the majority of respondents the utility independence assumption for SG and VAS did not hold. Similar to Bala et al., the results of this study indicated that preference weights as measured by SG and VAS techniques were not 'timeless'. Regardless of the preference measure used, both SG and VAS yielded higher scores when PCNV lasted for a shorter period of time.

A review of measurement of patient preferences for treatment outcomes after prostate cancer

The diagnosis of early-stage prostate cancer cases creates dilemmas for many men diagnosed with the disease each year. Treatment interventions are all associated with significant treatment morbidity, including impotence and incontinence. The basic concept behind patient preferences, or utilities, is to ask patients to make judgments about the value of particular health outcomes. Several preference-based instruments are available, including the visual analog rating scale, the time trade-off utility assessment, and the standard gamble. These assessments result in scores or weights assigned to different health states. From the perspective of the patient with prostate cancer, the treatment that produces optimal outcomes will depend on the relative importance of several domains, which may include pain, urinary functioning, sexual functioning, and general physical health. Patients with similar diagnoses and overlapping clinical characteristics may have markedly different preferences for treatment outcomes.

The distribution problem in economic evaluation: income and the valuation of costs and consequences of health care programmes

To date, a common view in the health economics literature is that the applicability of cost-benefit analysis (CBA) is limited, due to the distribution problem which underlies its main method of valuation (e.g. willingness to pay). One view is that cost effectiveness analysis (CEA) overcomes these problems. We show that the same distributional concerns apply to non-monetary valuations of health consequences, to measurement of costs and to the decision rules of CEA. Hence adopting CEA over CBA cannot be justified on the basis of "avoiding" distributional considerations. The implications of our results are discussed, including alternative strategies for the use of "income-based" research findings in social decision-making.

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

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

Differences in belief about likely outcomes account for differences in doctors' treatment preferences: but what accounts for the differences in belief?

Doctors, patients, and their relatives face a complex decision when there are multiple treatment options that differ in their profiles of risk and benefit over time. Doctors from a single specialist paediatric cardiac unit participated in a correlational study that used a novel tool (subjective multi-state survival graphs) to elicit their beliefs about the likely outcome of different treatments. Doctors' preferences were more closely related to their beliefs about long term, rather than short term, outcomes. This is consistent with placing greater value on far future than on immediate life years, highlighting the importance of incorporating patients' values for these outcomes into decisions of this kind. Beliefs about likely outcomes differed with whether or not doctors encountered former paediatric patients who were now adults, illustrating the difficulty of deciding what risk information should be available when the evidence base on outcomes is limited. Some problems of risk communication are identified, and the value of multi-state survival graphs as an aid to communication is discussed.

A comparison of three measures

We investigated the correlation between descriptive and valuational measures of health-related quality of life (HRQL) and assessed determinants affecting these measures. Our suspicion was that there is little similarity in the content of descriptive and valuational measures of HRQL. We thus conducted a cross-sectional observational study of 56 hemodialysis patients. All underwent structured interviews. Dependent variables were patients utilities [time trade-off (TTO)], global rating of HRQL and generic HRQL (SF-36). Independent variables were socioeconomic details, disease severity, comorbidity, symptoms, depression, social support, and laboratory data. The correlation between TTO and global HRQL was -0.33 (P = .0178) and between TTO and the SF-36 physical and mental summary scores -0.16 (P = .2383) and -0.20 (P = .1443), respectively. The regression models for the SF-36 physical and mental summary scores explained 75% and 64% of the variance, and for global HRQL 29% of the variance. The independent variables had no effect on the TTO. This confirmed our suspicion that a qualitative difference exists between TTO and descriptive quality of life tools. The TTO content could not be explained by the variables that entail the content of HRQL instruments.

Value of the time trade off method for measuring utilities in patients with rheumatoid arthritis

OBJECTIVE

To assess the feasibility, reliability, and validity of the time trade off (TTO) in patients with rheumatoid arthritis (RA).

METHODS

The TTO was applied in 194 patients with RA with increasing difficulty in performing activities of daily living. The test-retest reliability was determined in 35 of these patients and was calculated by the intraclass correlation coefficient (ICC). Construct validity was evaluated with the following sets of variables: measures of utility (rating scale), quality of life (RAND 36 item Health Status Survey (RAND-36) and RAQoL), functional status (Health Assessment Questionnaire, grip strength, and walk test), and disease activity (doctor's global assessment, disease activity score, pain, and morning stiffness).

RESULTS

Ten patients (5%) did not complete the TTO. The median value of the TTO was 0.77 (range 0.03-1. 0). The test-retest ICC of the TTO was 0.85 (p<0.001). Construct validity testing of the TTO showed poor to moderate correlations (Spearman's r(s) between 0.19 and 0.36, p<0.01) with all outcome measures except for the subscale role limitation (physical problem) of the RAND-36, the walk test, the doctor's global assessment of disease activity, and morning stiffness. Multiple regression analysis showed that only 17% of the variance of the TTO scores could be explained.

CONCLUSIONS

The TTO method appeared to be feasible and reliable in patients with RA. The poor to moderate correlations of the TTO with measures of quality of life, functional ability, and disease activity suggest that the TTO considers additional attributes of health status. This may have implications for the application of the TTO in clinical trials in patients with RA.

Validity and interpretation of preference-based measures of health-related quality of life

Utilities are numeric measurements that reflect an individual's beliefs about the desirableness of a health condition, willingness to take risks to gain health benefits, and preferences for time. This report discusses the approaches to assess and compare the validity of methods used to assign utilities for cost-utility analysis. Threats to validity include construct underrepresentation and construct-irrelevant variance. Construct underrepresentation occurs when a stimulus presented to a judge fails to fully represent the depth and complexity of information required in actual judgments. Construct-irrelevant variation occurs when factors irrelevant to preferences influence measurements of utilities. Among several factors that cause construct-irrelevant variation are cognitive abilities, numeracy skills, emotions and prejudices, and the elicitation procedure. Commonly used elicitation methods (visual-analog scales, time tradeoff, and standard gamble) capture different facets of utilities (desirableness of states, time preferences, and risk attitude) to different degrees. The validity of an elicitation protocol depends (1) on the degree to which its scaling method captures the relevant facets of utility and (2) on the degree to which measurements are influenced by construct-irrelevant variation. Discrete-state health index models provide an alternative to direct elicitation of utilities and work by attaching fixed preference weights to observable health states. The creation of discrete-state models with current technologies requires the adoption of strong assumptions about the scaling properties of utilities. Future research must refine methods of eliciting utilities and identify sources of construct-irrelevant variability that reduce the validity of utility assessments. Because of the impact of variation in techniques on measurements, we do not recommend the combination of utilities elicited with different protocols in cost-utility analysis and do not recommend the display of cost-utility ratios from different studies in comparison or "league" tables.

Exploring health preferences in sociodemographic and health related groups through the paired comparison of the items of the Nottingham health profile

BACKGROUND

Preference weighted measures of health related quality of life are necessary for cost effectiveness calculations involving quality of life adjustment. There are conflicting data about the influence of factors such as sociodemographic and health related variables on health preferences.

STUDY OBJECTIVE

The relative values attached to the items of the Spanish version of the Nottingham Health Profile (NHP) were assessed to make comparisons across social and health subgroups.

DESIGN AND PARTICIPANTS

Preference values were obtained in sets of 250 to 253 persons (total n=1258) using the method of paired comparisons after all possible pairs of NHP items had been presented to respondents for judgement of severity. chi(2) Tests and Spearman's correlations among item ranks were calculated.

MAIN RESULTS

Findings show that preferences elicited with the method of paired comparisons are consistent and independent of the sample from which they are obtained (mean correlation coefficients across subgroups range from 0.87 to 0.96). Conclusion-The evaluation of health did not seem to be related to sociodemographic variables (gender, age, social class) or to the health status of the respondents, suggesting that health preferences are stable across different populations.