Psychometric evaluation of the Fatigue Severity Scale in patients with major depression

This study aimed to investigate the psychometric properties of the Fatigue Severity Scale (FSS), a widely used unidimensional fatigue measure, in patients with major depression.

Subjects included were 72 patients with major depressive disorder, diagnosed with the DSM-IV based M.I.N.I. 5.0.0., without comorbid fatigue-associated conditions and Hamilton Depression Rating Scale (HDRS) scores ≥ 17 as well as 40 sex- and age-matched healthy controls. The FSS was administered to patients on two time points separated by a 1-week interval and to controls. The vitality subscale of the 36-item Short Form Health Survey (SF-36vit) and a visual analogue fatigue scale (VASF) were also administered.

A total of 79.2% of patients vs. 15% of controls were fatigue cases according to the M.I.N.I. fatigue/energy loss item. The distribution of FSS scores was negatively skewed in the patient group, demonstrating a ceiling effect. The FSS presented satisfactory test-retest reliability (intraclass correlation coefficient 0.993), internal consistency (Cronbach's α coefficient 0.947), concurrent validity (correlations with SF-36vit, VASF and HDRS were -0.52, 0.73 and 0.32, respectively) and discriminative validity between patients and controls. Factor analysis demonstrated a unidimensional structure. The optimal FSS cutoff score for clinically significant fatigue was 5.4 against the presence of fatigue/energy loss according to the M.I.N.I. as a 'gold standard'.

When administered to patients with major depression, the FSS was shown to have satisfactory psychometric properties with the exception of a ceiling effect, which may pose limitations to its use in this population.