How sure are you? — the properties of self-reported conviction in the elicitation of health preferences with discrete choice experiments

Discrete choice experiments (DCE) are often used to elicit preferences, for instance, in health preference research. However, DCEs only provide binary responses, whilst real-life choices are made with varying degrees of conviction. We aimed to verify whether eliciting self-reported convictions on a 0–100 scale adds meaningful information to the binary choice. Eighty three respondents stated their preferences for health states using DCE and the time trade-off method (TTO). In TTO, utility ranges were also elicited to account for preference imprecision. We verified the properties of the conviction across three areas: (1) response to various choice task modifications (e.g. dominance, increase in complexity, distance from the status quo) and association with rationality violations (e.g. intransitivity); (2) association with test–retest results; (3) relation to the utility difference and imprecision estimated in TTO. Regarding (1), conviction increased in choice tasks with lower complexity, larger relative attractiveness, and lower distance to the status quo. Regarding (2), choices made with above-median conviction were sustained in 90% of the cases, compared to 68% for below-median conviction. Regarding (3), the conviction increases with utility difference and it decreases with utility imprecision; overconfidence seems to prevail: non-zero conviction is reported even for identical utilities. Self-reported conviction in DCE is associated in an intuitive way with the observed choices. It may, therefore, be useful in explaining or predicting behaviour or bridging the gap between the results of various elicitation tasks.