Validation of a three-item Fatigue Severity Scale for patients with substance use disorder: a cohort study from Norway for the period 2016–2020

Abstract Background Little attention has been paid to customising fatigue questionnaires for patients with Substance Use Disorders (SUDs). The present study aims validate and shorten the nine-item Fatigue Severity Scale (FSS-9) Visual Analogue (VAFS) use this population. Methods We used data from a nested cohort annual health assessments responses on FSS-9 VAFS. During period 2016–2020, 917 were collected 655 SUD in Bergen Stavanger, Norway. A total of 225 answered assessment at least twice. defined baseline as first when sorted chronologically per patient. checked internal consistency, we longitudinal confirmatory factor analysis (CFA) linear mixed model (LMM) Results consistency was excellent Cronbach’s α 0.94 0.93 second assessment. When shortening three-item FSS (FSS-3, items 5–7), 0.87 0.84 not affected VAFS added FSS-3 FSS-9. CFA showed well-fitting (χ 2 = 13.33, degree freedom 8, P 0.101). LMM equal changes individual level (slope: 0.00, > 0.05) 0.01, between assessments. Conclusion could be shortened high validity reliability SUDs addition did provide much variability.