OBJECTIVES: To develop and clinimetrically validate the Brief Brain Fog Scale (BBFS), a concise self-report tool for assessing post-COVID-19 cognitive symptoms, and to evaluate its structural validity, reliability and precision.
METHODS: The BBFS was generated from literature and expert review and finalized as five items targeting core brain-fog symptoms.A total of 844 participants completed an online cross-sectional survey, including 686 with self-reported post-COVID brain fog and 158 healthy controls. Rasch modeling and Mokken scaling were used to examine unidimensionality, item fit, person reliability, and item scalability. Local independence and differential item functioning (DIF) were assessed across age, sex, and education groups.
RESULTS: The BBFS fit Rasch model expectations (χ = 44.6, df = 60, p = 0.928) and showed strong scalability (Mokken H = 0.679). Reliability was high (PSI = 0.846; WLE reliability = 0.846; EAP reliability = 0.852), with optimal precision in the moderate symptom range. All items had acceptable Infit MNSQ values (0.5-1.5), though several exhibited elevated Outfit in the highest response category. Local independence was largely supported; one pair marginally exceeded the indicative Q3threshold (0.204), and none exceeded 0.30. Uniform DIF was identified across age, sex, and education. Two items showed lower thresholds in older respondents, two showed higher thresholds in females, and four showed lower thresholds in postgraduate respondents. 'Forgetful' did not exhibit education-related DIF. 2 ⁎
CONCLUSIONS: The BBFS is a reliable, unidimensional instrument for post-COVID brain fog, with robust measurement properties supported by Rasch and Mokken analyses. Although some items showed demographic sensitivity, the total scale functioned consistently across groups. The BBFS represents a potentially valid and practical screening instrument. Future work should examine longitudinal responsiveness, cross-cultural generalizability, and item refinements.
Long Covid