Psychometric validation of the European Portuguese version of the Fatigue and Altered Cognition Scale (FACs)

Fatigue and "brain fog" are symptoms that may arise from lifestyle factors and various clinical conditions. Despite their significant impact on daily functioning, there is a lack of psychometrically robust instruments to measure their co-occurrence. The Fatigue and Altered Cognition Scale (FACs) was developed to address this gap, allowing the assessment of central fatigue and cognitive complaints commonly referred to as brain fog. In the present study, we translated, culturally adapted, and validated the FACs for European Portuguese. A sample of 591 Portuguese-speaking adults completed the Portuguese version of the FACs, along with the Burnout Assessment Tool (BAT) and the Depression, Anxiety, and Stress Scales (DASS). Confirmatory Factor Analysis tested the factorial structure, and internal consistency and convergent validity were also evaluated. A bifactor model demonstrated the presence of a general factor underlying all items. Internal consistency was excellent, and the FACs exhibited strong positive correlations with both the BAT and the DASS. Moreover, the FACs demonstrated strong criterion-related validity through its significant and robust associations with burnout, depression, anxiety, and stress. Our findings establish the FACs as a valid, reliable, and efficient instrument for both clinical and research applications within European Portuguese contexts.