Validating the Existential Quest Scale using item response theory

The Existential Quest Scale (EQS) is a brief instrument designed to assess individuals' willingness to engage with existential quest in both religious and secular contexts. As the construct of existential quest becomes increasingly relevant for understanding psychological flexibility, identity development, and social attitudes in multicultural societies, ensuring the validity of its measurement is essential. Previous validations of the EQS have relied on Classical Test Theory (CTT), which limits comparability across groups and item-level precision. This study aims to evaluate the EQS using Rasch modeling, a robust item response theory (IRT) approach that overcomes such limitations. Drawing on a large, heterogeneous sample (<i>N</i> = 4,378), we assessed dimensionality, item functioning, and measurement invariance across sex, age, and religious affiliation. Results confirmed the unidimensional structure of the EQS, its ability to discriminate levels of existential quest, and its psychometric invariance across demographic groups. Findings also suggested revisions to item and response category functioning to enhance scale performance. By applying IRT to the EQS, this study advances the psychometric assessment of complex, culturally adaptive constructs and supports the EQS as a rigorous tool for research and applied settings.