Factor Structure and Measurement Invariance of the Five Facet Mindfulness Questionnaire (FFMQ) in Participants Experiencing Psychosis

Mindfulness-based interventions (MBIs) are increasingly incorporated into treatments for psychosis. The Five Facet Mindfulness Questionnaire (FFMQ) is one of the most widely used self-report measures of trait mindfulness, yet its factor structure and measurement invariance have not been systematically evaluated in individuals experiencing psychosis. Existing research has relied heavily on non-clinical samples, item parceling, and limited modeling approaches, raising concerns about the interpretability of FFMQ scores in clinical contexts. The present study aims to examine the factor structure, construct validity, and measurement invariance of the FFMQ in individuals with psychosis compared to non-clinical controls. We will recruit 250 participants who identify as experiencing psychosis and 250 without psychosis from a large online sample. The study will employ exploratory structural equation modeling (ESEM), confirmatory factor analysis (CFA), and bifactor modeling to evaluate competing representations of the FFMQ, including models that account for item wording effects. Measurement invariance testing will assess whether the FFMQ operates equivalently across psychosis and non-psychosis groups, enabling meaningful comparisons. Construct validity will be examined through associations between mindfulness facets and related variables, including decentering, psychotic symptom severity, global functioning, cognitive failures, and affect. By clarifying whether the FFMQ measures mindfulness consistently in individuals with psychosis, this study addresses a gap in the literature. Findings will inform the appropriateness of using total and subscale scores in psychosis research, strengthen the methodological foundation of MBI outcome studies, and contribute to broader efforts to improve the validity of psychological assessment tools across diverse clinical populations.