Conference Agenda

Stated preference methods are central to non-market valuation but remain vulnerable to hypothetical bias, raising concerns about the credibility of resulting welfare estimates. This study provides a randomized, prospective evaluation of widely used ex-ante hypothetical bias mitigation techniques within a large discrete choice experiment (DCE) on coastal bathing-site management. The DCE is administered to 3,312 recreational users in the Gulf of Gdańsk and the Vistula Lagoon region and elicits willingness to travel for improvements in safety and information attributes, with travel distance serving as the numéraire. The experimental design varies four mitigation levers: (i) pre-task scripts (cheap talk, solemn oath, none), (ii) the presence of opt-out reminders, (iii) the position of the distance attribute within the choice task, and (iv) DCE menu size (two versus three alternatives). A novel embedded stress test choice featuring an extreme travel distance is used as an artificial indicator of respondents’ susceptibility to hypothetical bias. The results show that placing the distance attribute first consistently increases the share of respondents failing the stress test, suggesting that attempts to enhance cost salience through attribute ordering may backfire. Among the evaluated countermeasures, the solemn oath script performs best, substantially reducing the proportion of bias-prone respondents across both menu sizes. Cheap talk and opt-out reminders exhibit weaker and more context-dependent effects and, in some cases, prove counterproductive. Overall, the findings demonstrate that hypothetical mitigation techniques not only affect the prevalence of implausible responses but also shape baseline preferences and cost sensitivity. The study underscores the importance of careful experimental design and highlights solemn oath scripts as a particularly robust tool in non-monetary DCE contexts.