The Fatigue Questionnaire: Standardization in patients with major depression.

Fatigue measures have not been specifically standardized in depressed patients. This study aimed to investigate the reliability and validity of the 14-item Fatigue Questionnaire (FQ), a widely used multidimensional fatigue measure, in patients with major depression without comorbid fatigue-associated conditions. Subjects included were 81 patients with Major Depressive Disorder and Hamilton Depression Rating Scale (HDRS) scores > or = 15 without conditions associated with prominent fatigue and 40 sex- and age-matched healthy controls. The vitality subscale of the 36-item Short-Form Health Survey (SF-36vit) and a visual analogue fatigue scale (VASF) served as standards of reference for reported fatigue. The FQ presented satisfactory internal consistency (Cronbach's alpha coefficient 0.924), test-retest reliability (intraclass correlation coefficient 0.978), discriminant validity (between patients and controls) and concurrent validity (correlations with the SF-36vit and the VASF were -0.469 and 0.477, respectively). Factor analysis showed a two-factor structure (physical and mental fatigue), i.e. a structure similar to the one originally proposed. However, items 3 ('sleepiness'), 4 ('difficulty starting things') and 14 ('loss of interest') did not load on the factor expected. With these items removed, the derived 11-item version of the scale was shown to be a 'purer' measure of fatigue in depressed patients, independent of the severity of depression and comorbid sleepiness.