Measuring beliefs about free will: a critical review of the Free Will Inventory.

This review critically evaluates the Free Will Inventory (FWI), a 29-item self-report instrument assessing beliefs about free will, determinism, and dualism, by situating it within broader philosophical and psychological frameworks and prior attempts to measure free will beliefs. To identify relevant peer-reviewed studies, a structured literature search using systematic principles was conducted to locate research that has validated or critiqued the FWI. The review also considers how free will belief is conceptualised and operationalised within the FWI, and the implications this has for interpreting its scores. The reviewed evidence indicates generally acceptable internal reliability across multiple international samples, although no published studies have assessed test-retest reliability. Existing findings support aspects of construct, face, and content validity, while criterion validity remains largely unexplored, and several methodological considerations - including the potential influence of social desirability, demand characteristics, and cultural context - have been noted. Overall, the literature suggests that the FWI is a conceptually grounded and moderately reliable measure of free will beliefs, but further research is needed to clarify its temporal stability, cross-cultural robustness, practical applications, and the conceptual interpretation of its scores.