Sequence effects in time trade-off valuation of hypothetical health states.

Choice-based stated preference methods, such as time trade-offs (TTOs), are used to establish health state utilities informing healthcare allocation. However, little is known about the presence of (position-dependent and precedent-dependent) sequence effects in the valuation of health states, despite techniques requiring respondents to evaluate several health states in a sequence. This paper is the first to explicitly test for the presence of sequence effects in the health domain using a new explanation based on contrast effects and preference imprecision; the implication being that randomisation cannot avoid sequence effects. Six TTO questions were designed using the EQ-5D-3L descriptive system. These were grouped into two blocks of three and within each block four sequences were used. In an online survey, 1,197 Spanish respondents answered one grouping of three TTO questions. Results indicate that sequence effects can affect preferences as utilities of health states are biased downwards if preceded by a better health state and biased upwards if preceded by a worse health state. This study informs our understanding of how context effects interact with preference elicitation methods, which is essential for interpreting survey results used to inform policy.