Convergent validity in incentive-compatible contingent valuation: Bid-vector and elicitation format effects

: This study investigates convergent validity between elicitation formats within contingent valuation methodology, focusing on theory-driven formats designed to align with incentive compatibility. While earlier literature endorsed the single binary choice (SBC) format as the only incentive-compatible option, recent studies outline theoretical conditions under which payment card (PC) and open-ended (OE) formats may also encourage truthful preference revelation. We contribute to this debate by directly comparing these three theory-driven formats and assessing their robustness against bid-vector effects and other biases such as anchoring, yea-saying, and strategic misrepresentation. We conduct a large-scale, multi-country survey with 12,343 respondents across Poland, Sweden, Hungary, Spain, Germany, and the Netherlands, examining consumers’ willingness to pay (WTP) for an EU-wide biodiversity-enhancing program. The results indicate limited convergent validity across formats, with substantial discrepancies in WTP estimates. However, analysis of choice frequencies suggests that convergent validity holds for lower bid levels, whereas higher bids introduce differences. We argue that these differences stem from both behavioral biases and methodological factors, including bid vector design and econometric assumptions. Our results underscore the critical influence of bid structure on WTP estimates and highlight the need for further research to refine elicitation formats and econometric methods used in contingent valuation studies.