Understanding circularity knowledge across the general public–expert spectrum: Instrument development and cross-national evidence from six European countries

Circular Economy is increasingly recognized as a multidimensional transition necessary for resource efficiency in the built environment; however, its implementation is hindered by fragmentation. This study investigates the dynamics of circularity knowledge across the public-expert spectrum using a psychometrically validated instrument supported by Item Response Theory. Empirical data were collected from the Netherlands, Belgium, Poland, Türkiye, Romania, and Italy, representing diverse regulatory, educational, and economic settings. The results demonstrate that circularity knowledge is not a binary paradigm but a layered, permeable continuum. While professional participation and advanced higher education are significant determinants of higher circularity literacy, the study reveals a knowledge ladder effect where entry-level higher education provides limited benefits relative to the general public's knowledge levels. The instrument demonstrates robust targeting across the population, evidenced by a strong correlation (r = 0.812) between latent proficiency and raw scores, which pinpoints a significant transition threshold at 43.3 points that separates academic preparation from verified expert-level circularity literacy. It shows that although experts are well-calibrated, groups with lower knowledge initially exhibit significantly overconfidence, which only corrects after evaluation-focused reflection. Cross-country analysis confirms structural validity of the tool as a transferable latent construct and demonstrates that specialised curriculum integration leads to knowledge convergence regardless of national origin. It concludes that systemic curriculum integration, practice-based learning, and the use of diagnostic tools to harmonize stakeholder contributions in participatory settings (e.g., Urban Living Labs) are critical levers for accelerating the transition to a circular built environment.