Validation of Fatigue Impact Scale with various item sets – a Rasch analysis

Figures & data

Table 1. Characteristics of study population, n = 354.

	N (%)
Age, years, n = 350
≤54	201 (57.4)
55–69	111 (31.7)
≥70	38 (10.9)
Male/female, n = 352	184/168 (52.3/47.7)
Diagnosis, n = 354
Liver disease	222 (62.7)
Irritable bowel syndrome	132 (37.3)

Table 2. Comparative item sets of FIS versions based upon the FIS item number.

FIS item number and short name^a	Subscale	MFIS	D-FIS	FIS15	FIS6
1. I feel less alert	Cognitive	X	X
2. Isolated from social activities	Psychosocial
3. Reduced my workload	Psychosocial		X	X	X
4. I am more moody	Psychosocial
5. Difficulty paying attention	Cognitive	X
6. I feel like I cannot think clearly	Cognitive	X
7. I work less effectively	Psychosocial
8. Rely on others to help me	Psychosocial
9. Difficulty planning activities	Psychosocial			X
10. More clumsy and uncoordinated	Physical	X		X	X
11. I am more forgetful	Cognitive	X
12. More irritable and angered	Psychosocial
13. Careful about physical activities	Physical	X
14. Less motivated to do physical effort	Physical	X	X
15. Engage in social activities	Psychosocial	X		X
16. Ability to travel outside home	Psychosocial	X		X
17. Trouble maintaining physical effort	Physical	X	X
18. Difficult to make decisions	Cognitive	X	X	X	X
19. Few social contacts outside home	Psychosocial
20. Normal events are stressful	Psychosocial			X
21. Less motivated to do thinking	Cognitive	X
22. Avoid stressful situations	Psychosocial			X
23. Muscles feel weak	Physical	X
24. Increased physical discomfort	Physical	X		X	X
25. Difficulty dealing with anything new	Psychosocial			X
26. Ability for thinking tasks	Cognitive	X	X
27. Ability to meet demands	Psychosocial
28. Ability to provide financial support	Psychosocial			X
29. Engage in sexual activity	Psychosocial
30. Difficult to organize thoughts	Cognitive	X		X	X
31. Ability for physical tasks	Physical	X
32. Worry how I look to other people	Physical			X
33. Less able to deal with emotional issues	Psychosocial
34. Feel slowed down in my thinking	Cognitive	X	X
35. I find it hard to concentrate	Cognitive	X
36. Participating in family activities	Psychosocial			X
37. Limited physical activities	Physical	X	X
38. More or longer periods of rest	Physical	X		X	X
39. Unable to provide emotional support	Psychosocial
40. Minor difficulties get major	Psychosocial

^a All items start with: Because of my fatigue….

Table 3. Fatigue Impact Scale (FIS): summary of Rasch analysis.

	Item residual		Person residual		Chi square interaction
Analysis	Mean	SD	Mean	SD	Value	df	p	α	t-Test % (LCI)	% at floor
FIS	–0.208	1.678	–0.340	1.920	331.8	200	0.0000	0.94	22.3 (19.9)	11.3
FIS-3	–0.516	2.156	–0.516	1.024	27.2	21	0.1631	0.84	3.5 (0.9)	11.3
FIS-3(dif)	–0.065	1.336	–0.463	0.995	35.9	42	0.7351	0.96	NA	11.3
MFIS	–0.291	0.925	–0.403	1.587	93.6	105	0.7806	0.97	24.7 (22.3)	11.9
MFIS-3	–0.214	1.338	–0.415	0.939	33.8	15	0.0037	0.78	4.7 (2.1)	11.9
MFIS-3(dif)	0.198	0.966	–0.405	0.938	40.5	25	0.0267	0.80	NA	11.9
D-FIS	–0.525	1.157	–0.360	1.072	36.4	40	0.6320	0.85	9.7 (7.3)	17.5
FIS15	–0.525	1.536	–0.408	1.316	67.7	75	0.7140	0.92	7.3 (4.9)	15.2
FIS6	–0.345	0.625	–0.341	1.032	28.3	30	0.5551	0.89	6.5(4.0)	20.0
Ideal values	0.0	1.0	0.0	1.0			>0.05^a	>0.7	(LCI <5.0)

^a Bonferroni adjusted, LCI: lower confidence interval; NA: not applicable.

Figure 1. Operational ranges of raw scores of various FIS versions.

Figure 2. Person-item threshold distribution for FIS15.