Exploring Differences between TTO and DCE in the Valuation of Health States.

There is recent interest in using discrete choice experiments (DCEs) to derive health state utility values, and results can differ from time tradeoff (TTO). Clearly, DCE is "choice based," whereas TTO is generally considered a "matching" task. We explore whether procedural adaptations to the TTO, which make the method more closely resemble a DCE, make TTO and choice converge. In particular, we test whether making the matching procedure in TTO less "transparent" to the respondent reduces disparities between TTO and DCE. We designed an interactive survey that was hosted on the Internet, and 2022 interviews were achieved in the United Kingdom in a representative sample of the population. We found a marked divergence between TTO and DCE, but this was not related to the "transparency" of the TTO procedure. We conclude that a difference in the error structure between TTO and choice and that factors other than differences in utility are affecting choices is driving the divergence. The latter has fundamental implications for the way choice data are analyzed and interpreted.

Are people unrealistically optimistic? It depends how you ask them.

OBJECTIVE: The present study investigated the extent to which direct (D) and indirect (ID) measures of unrealistic optimism truly capture people's beliefs about their comparative risk status. METHODS: Respondents (N = 425) were contacted in a general population survey. The D measure required respondents to estimate whether their personal chance of contracting an illness was above/below the average for people of the same age/gender. The ID measure was based on separate assessments of personal/others' chances. RESULTS: Poor concurrent validity between the measures implied that one or both was tapping into perceptions unrelated to comparative risk. This was explored by examining the relationships between the measures and various health problem attributes (e.g. perceived preventability,personal experience). A picture emerged that suggested the D measure did not seem to reflect the effects of social comparison as much as the ID measure, a crucial criterion for a measure intended to elicit comparative risk ratings. CONCLUSION: When measuring unrealistic optimism by asking 'Compared to other men/women your age how would you rate your chances of X?' researchers should be sensitive to the possibility that the question is being interpreted simply as 'How would you rate your chances of X?'.