Fig. 2
From: Evaluating the psychometric properties of the fatigue severity scale using item response theory
Boxplot of the Multidimensional Fatigue Inventory and the Fatigue Severity Scale by sleep duration group. MFI: Multidimensional Fatigue Inventory, FSS: Fatigue Severity Scale. Legend for sleep: 1, less than 4 h; 2, 4–5 h; 3, 5–6 h; 7, 9 h or more. The sleep duration indicated on the right side of the hyphen is not included in the group but is included in the next group (i.e., Group 2 included the persons who had 4 or more and less than 5 h of sleep). * p < .05, ** p < .01, *** p < .001