Purpose: There is concern that the tasks involved in the standard gamble and time trade off (TTO) are too complex for certain populations. The objective of this study is to explore a novel application of the Discrete Choice Experiment (DCE) that resembles the Time Trade Off (TTO) task to estimate values on the full health – dead scale for the EQ-5D.
Method: The DCE is tested in a web survey alongside the TTO by inviting 4189 members of a market research panel in Canada to participate in an internet based survey. The DCE was designed to closely resemble the TTO task describing two health states each with a given survival. The DCE requires respondents to answer which health state they prefer, not the degree they prefer a health state as is required in the TTO. Experimental design theory was used to develop 144 choice sets which enable the interaction between survival and each EQ-5D attribute to be estimated. Conditional and mixed logit models were used to analyse DCE results, and values were converted to the full health – dead scale. The TTO design and analysis followed existing EQ-5D valuation studies. Values from the two techniques are compared along with other issues such as rates of completion, failure to engage and understand the task and self reported ease of understanding and answering.
Results: Of the 1400 (33%) that responded to the survey, their socio-demographic profiles were largely representative of the Canadian general population. Over 13% of respondents failed to complete the 5 TTO tasks compared to 4% for the 8 DCE tasks. Over a third of the completers of the TTO appeared to fail to understand or engage with the task. The inclusion of these values in final models dramatically influenced average values. In contrast, the DCE results were robust to all completed values.
Conclusion: The study finds that the new DCE is able to derive logical and consistent values for health states valued on the full health – dead scale. The DCE overcame some issues identified in the version of TTO currently used to value EQ-5D, notably whether to exclude respondents who fail to understand the task and incorporating values considered worse than dead without transformation. This has important implications for providing values that represent the preferences of all respondents.
Candidate for the Lee B. Lusted Student Prize Competition