Future research

Comparison of previous EQ-5D-3L value sets with the more recently developed EQ-5D-5L value set within countries has commenced. However, the fact that population preferences for EQ-5D-3L health states were collected, in many cases, more than 20 years ago, has not been considered [19]. In the specific case of Spain, the time difference between studies was around 12 years and, as shown in chapters 2 and 9, differences with respect to the relative importance of dimensions occurred. One could argue that these differences were only due to differences in the instruments or in the valuation methods used. However, as discussed in chapter 9, it seems that these were not the only issues, at least in Spain where the economic crisis appears to have had an important impact in how the population views health problems.

As the economic crisis has been worldwide, and has not only occurred in Spain, it is worth considering whether the Spanish case can be safely extrapolated to any other country.

However, another reason can partially explain the observed differences. It may have been that the policies implemented to make the life of physically disabled people easier have had an impact on how the population views mobility-related problems, which could explain the reduction in the relative importance of the mobility dimension. Having stated this, and given the uncertainty concerning what really influences the population to change its health preferences, then the development of a value set necessitates a longitudinal approach rather than a transversal one. In other words, valuation studies for a specific instrument should be performed at least each 5-10 years, the exact time being related to the number of policy changes made in the country.

The remaining question is whether exactly the same method should be used again. In principle the response should be: “no”, as there is always room for improvement. For example, even when explained well, the C-TTO task remains complex for respondents to carry out.

One of the most difficult aspects of the task for the respondent is to give a precise value “t”

for her/his point of indifference when choosing between 10 years in an impaired state and t years in full health. This can lead respondents to exhibit behavioural imprecision (satisficing, circling, and wandering) which will reduce the accuracy of their C-TTO responses. Satisficing is arguably the most problematic: once respondents start to feel that the choices are becoming difficult to make, they press the “A&B are about the same” button to terminate the task, instead of continuing until they reach their “true” point of indifference. Satisficing can thus lead to inaccurate preferences being recorded by respondents, which may bias modelling results.

While some respondents may be struggling to determine their indifference point, they might be capable of reporting their indifference range of values for a health state more accurately.

In addition to the behavioural imprecision of the respondent’s data, the C-TTO task itself also inhibits a degree of imprecision (i.e., task imprecision) as only year and half-year values of t are included in the iteration sequence, leading to 41 discrete values, rather than a continuous range of values. Changing the termination rule in C-TTO (i.e., removing the obligation to

184 | Chapter 10

As the economic crisis has been worldwide, and has not only occurred in Spain, it is worth considering whether the Spanish case can be safely extrapolated to any other country.

One of the most difficult aspects of the task for the respondent is to give a precise value “t”

While some respondents may be struggling to determine their indifference point, they might be capable of reporting their indifference range of values for a health state more accurately.

Discussion | 185

10

provide an indifference point) may reduce behavioural and TTO task imprecision. I have proposed to change the current termination rule of the TTO by utilizing the following two conditions: 1) A fixed number of steps in the iterative sequence, and 2) “A specific” interval of the range of values where the true preference is, e.g,. when a respondent is circling between values of a width of 1 year. Hence, the future of C-TTO tasks should be interval-based instead of based on indifference points.

Conclusions

The studies presented in this thesis, together with similar work accomplished elsewhere, have resulted in a detailed valuation protocol for the EQ-5D-5L instrument, paired with a quality assurance procedure and novel analytical approaches. The updated protocol has enabled teams from all over the world to successfully establish EQ-5D-5L value sets.

Despite TTO being a preferred method for health state valuation for two decades, important new insights have been achieved concerning how respondent behaviour and specific features of the valuation task work together to define the level of precision of C-TTO responses. These insights have emphasized the importance of the interviewer’s role in C-TTO valuation, and made it evident that it is unlikely that any interview protocol or software for performing interviews is sufficient to guarantee proper interviewer competence, compliance, or engagement. This motivated the introduction of a QC process and of new modelling approaches. Looking back, one may wonder how widespread similar issues were in other valuation studies, and why they have not been identified (and resolved) previously. Most likely, similar issues have always been there, but were simply not noticed.

Given the changes in thinking concerning what works in valuation exercises, it would be appropriate to recognize that – at least from a valuation perspective – the rigorous approach to EQ-5D-5L valuation studies inspires trust. However, it can also be noted that the kind of insights that guide our current valuation work did not exist when EQ-5D-3L was originally valued. It is wise to remain modest with respect to claims about the qualities of older value sets derived from instruments such as EQ-5D-3L, SF-6D, AQoL and HUI, until we have returned to scrutinize them. Such research is warranted to provide users, stakeholders and society with recommendations regarding the use of the instruments in analysis and health care decision-making, to the benefit of all patients.

Discussion | 185

10 Conclusions

186 | Chapter 10

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