The 18-item Lee Fatigue Scale (LFS)[40]measured perceived fatigue. Scale items were
rated from 1 to 10, anchored with extremes relevant to the specific items, e.g., 1 ‘not all
tired’ to 10 ‘extremely tired.’ The LFS was developed for use in sleep disorder research and
originally used a visual analog scale. It has been used subsequently with a numeric rating
scale and in a variety of populations with various chronic diseases. It has demonstrated
strong internal consistency reliability (Cronbach alpha of .91–.96 across different
populations for both the full scale and the subscales[40, 41],and good sensitivity todiscriminate within subject changes. Concurrent validity has been demonstrated with high
correlations between the LFS and the Stanford Sleepiness Scale [40] and the Profile of
Mood States [40, 41].