A consistency test of the time trade-off

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

The Time Trade-Off Method: An Exploratory Study

In a pilot study we investigate whether the inferences we draw about people's preferences towards health care treatments are altered if we vary the procedure that is used to elicit these preferences. In a conventional Time Trade-Off question, respondents express their preferences towards treatment by comparing a period of ill-health with a shorter period in a higher quality of life. In our less conventional TTO question, we vary the procedure by asking respondents their preferences towards treatment by comparing a period of ill-health with a longer period in a lower quality of life. The quantitative data is equivocal about whether preferences for treatment differ between the conventional and unconventional questions. The qualitative data support the notion of contrasting issues in questions that involve prolonging time in a more severe quality of life and appear to account for a failure to find quantitative differences in all of the questions.Time Trade-Off, Procedural invariance

Construct validity of the interview Time Trade-Off and computer Time Trade-Off in patients with rheumatoid arthritis: A cross-sectional observational pilot study

Background\ud The Time Trade-Off (TTO) is a widely used instrument for valuing preference-based health-related quality of life (HRQoL). The TTO reveals preferences for own current health (‘utilities’) on a scale anchored between death (0) and perfect health (1). Limited information on the external validity of the TTO is available. Aim of this pilot study was to examine the construct validity of both an interview TTO and a computer-based TTO in patients with rheumatoid arthritis (RA).\ud \ud Methods\ud Thirty patients visiting the outpatient rheumatology clinic participated. Construct validity was assessed by measuring convergent and discriminative validity. Convergent validity was assessed by calculating Spearman’s correlations between the utilities obtained from the TTOs and pain, general health (rating scales), health-related quality of life (SF-36 and SF-6D) and functional status (HAQ-DI). Discriminative power of both TTO measures was determined by comparing median utilities between worse and better health outcomes.\ud \ud Results\ud Correlations of both TTO measures with HRQoL, general health, pain and functional status were poor (absolute values ranging from .05 to .26). Both TTOs appeared to have no discriminative value among groups of RA patients who had a worse or better health status defined by six health outcome measures. About one-third of respondents were zero-traders on each of the TTO measures. After excluding zero-traders from analysis, the correlations improved considerably.\ud \ud Conclusions\ud Both the interview TTO and computer TTO showed poor construct validity in RA patients when using measures of HRQol, general health, pain and functional status as reference measures. Possibly, the validity of the TTO improves when using an anchor that is more realistic to RA patients than the anchor ‘death’

Testing the predective validity of the time trade-off and the Stardard Gamble

This paper tests the consistency of health utility measurements with individual preferences. We compare three methods, the time trade-off, the standard gamble and a version of the standard gamble that corrects for the deviations from expected utility modelled by prospect theory. Individual preferences are measured both through a ranking task and through a choice task. In decisions involving no risk the time trade-off is most consistent with people’s preferences with the standard gamble a close second. In decisions involving risk the corrected standard gamble is most consistent with people’s preferences. Our data do not support the common assumption in health economics that utility is transferable across decision contexts.Health utility measurement, QALYs,stardard gamble, time trade-off, prospect theory.

The Implications of Linking Questions within the SG and TTO Methods

We consider the impact of introducing intermediate stages, chained together, into the Standard Gamble (SG) and Time Trade-Off (TTO) methods. We broadly replicate the patterns of responses observed in other SG studies. Less is known about the impact of intermediate stages, chained together, in the TTO method. We find that the TTO responses do not replicate the patterns found in the SG responses. We discuss additional issues that are brought to bear in the TTO responses compared to the SG responses and consider whether these can account for the different results.Standard Gamble, Time Trade-Off, Chaining

A comparison of United States and United Kingdom EQ-5D health states valuations using a nonparametric Bayesian method

Few studies have compared preference values of health states obtained in different countries. This paper applies a nonparametric model to estimate and compare EQ-5D health state valuation data obtained from two countries using Bayesian methods. The data set is the US and UK EQ-5D valuation studies where a sample of 42 states defined by the EQ-5D was valued by representative samples of the general population from each country using the time trade-off technique. We estimate a function applicable across both countries which explicitly accounts for the differences between them, and is estimated using the data from both countries. The paper discusses the implications of these results for future applications of the EQ-5D and further work in this field.preference-based health measure; nonparametric methods; time trade-off; EQ-5D

THE LEAD TIME TRADE-OFF: THE CASE OF HEALTH STATES BETTER THAN DEATH

The Lead Time Trade-Off (L-TTO) is a variant of the TTO method that tries to overcome some of the problems of the most widely used method (Torrance, 1986) for health states worse than death (SWD). Theoretically, the new method reduces the problems that have been detected when researchers have elicited preferences for SWD. However, several questions remain to be clarified. One of them is the influence of this new method for states better than death (SBD). In this paper we try to shed some light on this issue using a split sample design (n=500). One subsample (n=188) was interviewed using L-TTO and the rest using the traditional TTO (T-TTO). Our results show that the L-TTO produces utilities that are consistently higher than the T-TTO for SBD. Furthermore, the higher the severity the higher the difference between both methods. Another finding is that the L-TTO seems to produce a lower number of SWD. This effect seems to be concentrated in the most severe health states. This implies a violation of additive separability, one of the cornerstones of the QALY model. Our data show that the L-TTO may be different from the T-TTO in more respects than those that were originally intended.Lead Time Trade-Off, QALYs, Discounting, Additive Independece

THE LEAD TIME TRADE-OFF: THE CASE OF HEALTH STATES BETTER THAN DEATH

The Lead Time Trade-Off (L-TTO) is a variant of the TTO method that tries to overcome some of the problems of the most widely used method (Torrance, 1986) for health states worse than death (SWD). Theoretically, the new method reduces the problems that have been detected when researchers have elicited preferences for SWD. However, several questions remain to be clarified. One of them is the influence of this new method for states better than death (SBD). In this paper we try to shed some light on this issue using a split sample design (n=500). One subsample (n=188) was interviewed using L-TTO and the rest using the traditional TTO (T-TTO). Our results show that the L-TTO produces utilities that are consistently higher than the T-TTO for SBD. Furthermore, the higher the severity the higher the difference between both methods. Another finding is that the L-TTO seems to produce a lower number of SWD. This effect seems to be concentrated in the most severe health states. This implies a violation of additive separability, one of the cornerstones of the QALY model. Our data show that the L-TTO may be different from the T-TTO in more respects than those that were originally intended.Lead Time Trade-Off, QALYs, Discounting, Additive Independece

Using rank and discrete choice data to estimate health state utility values on the QALY scale

Objective: Recent years has seen increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to conventional methods such as standard gamble and time trade-off. However, in order to use these health state values in cost effectiveness analysis using cost per quality adjusted life year (QALY) analysis, these values must be anchored on the full health-dead scale. This study addresses this challenge and examines how rank and discrete choice experiment data can be used to elicit health state utility values anchored on the full health-dead scale and compares the results to time trade-off (TTO) results. Methods: Two valuation studies were conducted using identical methods for two health state classification systems: asthma and overactive bladder. Each valuation study involved interviews of 300 members of the general population using ranking and TTO plus a postal survey using discrete choice experiment sent to all consenting interviewees and a "cold" sample of the general population who were not interviewed. Results: Overall DCE produced different results to ranking and time trade-off, whereas ranking produced similar results to TTO in one study, but not the other. Conclusions: Ordinal methods offer a promising alternative to conventional cardinal methods of standard gamble and TTO. However, the results do not appear to be robust across different health state classification systems and potentially different medical conditions. There remains a large and important research agenda to address

Using rank and discrete choice data to estimate health state utility values on the QALY scale

Objective: Recent years have seen increasing interest in the use of ordinal methods to elicit health state utility values as an alternative to conventional methods such as standard gamble and time trade-off. However, in order to use these health state values in cost effectiveness analysis using cost per quality adjusted life year (QALY) analysis, these values must be anchored on the full health-dead scale. This study addresses this challenge and examines how rank and discrete choice experiment data can be used to elicit health state utility values anchored on the full health-dead scale and compares the results to time trade-off (TTO) results. Methods: Two valuation studies were conducted using identical methods for two health state classification systems: asthma and overactive bladder. Each valuation study involved interviews of 300 members of the general population using ranking and TTO plus a postal survey using discrete choice experiment sent to all consenting interviewees and a "cold" sample of the general population who were not interviewed. Results: Overall DCE produced different results from ranking and time trade-off, whereas ranking produced similar results to TTO in one study, but not the other. Conclusions: Ordinal methods offer a promising alternative to conventional cardinal methods of standard gamble and TTO. However, the results do not appear to be robust across different health state classification systems and potentially different medical conditions. There remains a large and important research agenda to address.ranking; discrete choice experiment; preference-based measures; QALYs