Validity and reliability of a scale to assess fatigue.

A visual analogue scale to evaluate fatigue severity (VAS-F) was developed and tested in a sample of 75 healthy individuals and a sample of 57 patients undergoing medical evaluation for sleep disorders. The scale consists of 18 items related to fatigue and energy, has simple instructions, and is completed with minimal time and effort. The VAS-F compares favorably with the Stanford Sleepiness Scale and the Profile of Mood States, and its internal consistency reliabilities are high. Healthy subjects demonstrated significant differences between their evening and morning scores on the VAS-F, while sleep-disordered patients did not.