The extremity function index (EFI), a disability severity measure for neuromuscular diseases: psychometric evaluation

Figures & data

Table 1. Sample characteristics (n = 702).

Variables	Total sample
Gender (%)
Female	350 (50.1)
Age
Median	61
IQR	21
Mean (SD)	58.9 (15.7)
Range	19–92
Year since diagnosis
Median	7
IQR	11
Mean (SD)	11.6 (11.0)
Range	0-65
Relationship status (%)
Married/partnership	497 (70.8)
Unmarried/widowed/divorced	186 (26.5)
Missing	19 (2.7)
Educational level (%)
Primary school/vocational training	235 (33)
Secondary school/vocational training	270 (38)
Higher education/vocational training	161 (23)
University	28 (4)
Employment status (more answers possible) (%)
Enrolled in a training program or educational course	36 (5.1)
Employment (part time or full time)	173 (24.6)
Voluntary work (part time or full time)	42 (6.0)
(Partially) retired due to NMD	213 (30.3)
Housewife/househusband	171 (24.4)
Retired due to age	243 (34.6)
NMD category (%)
Motor neuron disorder	43 (6.1)
Muscle disorder	154 (22.1)
Junction disorder	234 (33.3)
Peripheral nerve disorder	271 (38.5)

IQR: inter quartile range (Q3-Q1).

Table 2. Factor loadings of the extremity function index (EFI) model.

		Factor
Upper Extremity Function Index
1	Any of the activities involved in your usual work, housework, or schoolwork	0.860
2	Your usual hobbies, and recreational or sporting activities	0.766
3	Lifting a bag of groceries to waist level	0.928
4	Lifting a bag of groceries above your head	0.900
5	Grooming your hair	0.829
6	Pushing up on your hands (e.g., from bathtub or chair)	0.855
7	Preparing food (e.g., peeling, cutting)	0.861
8	Driving	0.755
9	Vacuuming, sweeping, or raking	0.920
10	Dressing	0.915
11	Buttoning your clothing	0.839
12	Using tools or appliances	0.871
13	Opening doors	0.867
14	Cleaning	0.919
15	Tying or lacing shoes	0.883
16	Sleeping	0.494
17	Laundering clothes (e.g., washing, ironing, folding)	0.884
18	Opening a jar	0.810
19	Throwing a ball	0.846
20	Carrying a small suitcase (with your affected limb)	0.889
Lower Extremity Function Index
1	Any of the activities involved in your usual work, housework, or schoolwork	0.897
2	Your usual hobbies, and recreational or sporting activities	0.809
3	Getting into or out of the bathtub	0.889
4	Walking between rooms	0.924
5	Putting on your shoes or socks	0.894
6	Squatting	0.886
7	Lifting an object, like a bag of groceries from the floor	0.914
8	Performing light activities around your home	0.928
9	Performing intensive activities around your home	0.927
10	Getting into or out of a car	0.873
11	Walking 10 yards	0.924
12	Walking 200 yards	0.897
13	Going up or down 10 stairs (about 1 flight of stairs)	0.897
14	Standing for 1 hour	0.859
15	Sitting for 1 hour	0.623
16	Running on even ground	0.886
17	Running on uneven ground	0.905
18	Making sharp turns while running fast	0.933
19	Jumping	0.943
20	Rolling over in bed	0.828

Table 3. Scale features of the EFI total scale and subscales UEFI and LEFI (n = 702).

Sample and Scales	Cases (n)	Items (k)	Possible score range	Observed score range	Floor effect (%)	Ceiling effect (%)	Median	IQR	Mean	SD	Alpha
Total
EFI	702	40	0-160	0-159	5.6	0.0	37	41	37.8	25.8	0.98
UEFI	701	20	0-80	0-79	9.1	0.0	31	42	33.9	25.7	0.97
LEFI	700	20	0-80	0-80	8.4	0.6	41	48	41.7	28.2	0.97
Motor neuron disorder
EFI	43	40	0-160	0-158	2.3	0.0	54	49	55.1	28.2	0.98
UEFI	43	20	0-80	0-79	2.3	0.0	49	47	52.4	27.9	0.97
LEFI	43	20	0-80	0-80	4.7	4.7	61	50	57.4	32.1	0.98
Muscle disorder
EFI	155	40	0–160	0–159	1.3	0.0	49	67	50.8	25.7	0.98
UEFI	154	20	0–80	0–79	3.2	0.0	44	40	46.1	26.4	0.97
LEFI	153	20	0–80	0–80	1.9	1.3	56	42	55.6	27.4	0.97
Junction disorder
EFI	234	40	0–160	0–143	11.5	0.0	23	37	26.9	22.4	0.98
UEFI	234	20	0–80	0–72	14.1	0.0	25	36	26.8	22.3	0.96
LEFI	234	20	0–80	0–71	17.1	0.0	23	40	27.0	24.1	0.97
Peripheral nerve disorder
EFI	270	40	0–160	0–152	3.7	0.0	36	37	37.1	23.3	0.98
UEFI	270	20	0–80	0–76	9.3	0.0	27	40	30.2	23.9	0.96
LEFI	270	20	0–80	0–76	5.2	0.0	44	38	44.0	25.2	0.97

EFI: extremity function index; IQR: inter quartile range (Q3-Q1); LEFI: lower extremity functional index; SD: standard deviation; UEFI: upper extremity functional index.

Table 4. Known-groups validity of the extremity function index (n = 702).

	Low (0–4) versus high (5–10) extent of limitations					Poor (1–3) versus good (4–5) quality of life
	N Low/High	Low Mean Rank	High Mean Rank	p value (Z-statistic)^a	Effect Size	N Low/High	Poor Mean Rank	Good Mean Rank	p value (Z-statistic)^a	Effect Size
Extremity Function Index	278/424	216.4	440.1	0.000 (−14.3)	0.54	228/474	453.8	302.3	0.000 (−9.3)	0.35
Lower Extremity Function Index	278/422	215.3	439.6	0.000 (−14.4)	0.54	228/472	443.1	305.8	0.000 (−8.4)	0.32
Upper Extremity Function Index	278/423	230.5	430.3	0.000 (−12.8)	0.48	228/473	453.1	301.8	0.000 (−9.3)	0.35

^a Mann–Whitney U-test, 2-sided.

Table 5. Results of convergent and divergent validity of EFI total and subscales (n = 702).

	EFI^a	UEFI^a	LEFI^a
NMDIP
Muscle functions	0.73	0.63	0.74
Movement functions	0.59	0.50	0.59
Swallowing and speech functions	0.31	0.35	0.25
Excretion and reproductive functions	0.46	0.44	0.42
Mental functions and pain	0.58	0.56	0.53
Activities of moving around	0.82	0.69	0.86
Self-care and domestic activities	0.85	0.83	0.80
Participation in life situations	0.64	0.56	0.64
SF-36
Physical functioning	−0.89	−0.76	−0.92 **
Social functioning	−0.53	−0.52	−0.49
Role physical	−0.51	−0.49	−0.47
Bodily pain	−0.48	−0.44	−0.48
General health	−0.58	−0.55	−0.53
Mental health	−0.29	−0.32	−0.25
Role emotional	−0.32	−0.33	−0.28
Vitality	−0.49	−0.52	−0.42
GARS
Instrumental activities of daily living	0.89	0.83	0.86
Activities of daily living	0.86	0.77	0.87

^a Spearman rank order correlation coefficient, all correlations are significant at the 0.01 level (2-tailed).

EFI: Extremity Function Index; GARS: Groningen Activity Restriction Scale; LEFI: Lower Extremity Functional Index; NMDIP: Neuromuscular Disease Impact Profile; UEFI = Upper SF-36: Medical Outcome Study Short Form Questionnaire;

Expected convergent validity scores (higher correlations >0.70) in bold and expected divergent validity scores (lower correlations <0.40) in italic.

Table 6. Relative validity (RV) of the EFI, disease specific, domain specific and generic measurement instruments compared, using subgroups of extent of limitations (n = 702).

	Group A No to Low Extent of Limitations (score 0–4)		Group B Moderate Extent of Limitations (score 5–6)		Group C High Extent of Limitations (score 7–8)		Group D Very high Extent of Limitations (score 9–10)
	N	Median (IQR)	N	Median (IQR)	N	Median (IQR)	N	Median (IQR)	Chi Square	RV	A-B	B-C	C-D	A-D
Extremity Function Index (EFI)	278	16 (28)	169	39 (28)	197	51 (29)	58	79 (30)	258.0	96	0.43	0.23	0.42	0.59
Lower Extremity Function Index (LEFI)	278	18 (33)	167	44 (31)	197	59 (34)	58	84 (26)	268.8	100	0.41	0.26	0.45	0.61
Upper Extremity Function Index (UEFI)	278	14 (27)	168	38 (31)	197	44 (34)	58	74 (43)	201.5	75	0.39	0.17	0.36	0.54
NMDIP
Muscle functions	249	25 (26)	161	50 (25)	192	50 (25)	56	75 (37)	244.6	91	0.40	0.26	0.43	0.63
Movement functions	235	8 (17)	140	17 (25)	170	25 (16)	49	42 (29)	141.2	53	0.29	0.20	0.29	0.51
Swallowing and speech functions	270	0 (0)	156	0 (13)	188	0 (25)	55	13 (25)	57.3	21	0.22	–	0.18	0.37
Excretion and reproductive functions	206	0 (17)	120	8 (25)	140	17 (31)	43	25 (25)	55.5	21	0.20	–	–	0.37
Mental functions and pain	237	10 (15)	137	20 (20)	173	30 (25)	50	33 (25)	135.7	50	0.29	0.23	0.19	0.47
Activities of moving around	278	6 (17)	169	17 (22)	197	22 (28)	58	56 (34)	216.3	80	0.37	0.22	0.40	0.58
Self-care and domestic activities	277	4 (4)	169	17 (21)	197	29 (45)	58	75 (67)	254.6	95	0.41	0.25	0.40	0.61
Participation in life situations	276	0 (8)	168	8 (17)	196	17 (33)	55	33 (33)	189.1	70	0.26	0.29	0.28	0.60
SF-36
Physical functioning	277	25 (9)	169	19 (8)	197	16 (8)	58	11 (3)	254.7	95	0.39	0.26	0.44	0.61
Social functioning	278	9 (2)	169	8 (2)	196	7 (1)	58	6 (4)	130.6	49	0.27	0.19	0.21	0.43
Role physical	278	8 (3)	168	5 (4)	196	5 (2)	57	4 (2)	112.1	42	0.30	–	–	0.41
Emotional functioning	278	6 (1)	167	6 (2)	196	6 (2)	57	4 (3)	33.0	12	0.18	–	0.16	0.28
Mental functioning	278	25 (4)	169	24 (5)	196	24 (4)	58	22 (7)	32.4	12	0.13	–	0.16	0.27
Vitality	278	17 (6)	169	15 (5)	196	14 (5)	58	11 (6)	101.4	38	0.25	0.13	0.23	0.41
General health	278	17 (6)	169	14 (5)	196	12 (5)	58	10 (5)	169.7	63	0.35	0.22	0.20	0.48
Bodily pain	278	55 (16)	169	44 (17)	197	39 (20)	58	33 (22)	91.5	34	0.23	0.16	0.18	0.39
GARS
Activities of daily living	278	11 (4)	169	15 (7)	197	18 (10)	58	27 (17)	213.3	79	0.37	0.21	0.40	0.60
Instrumental activities of daily living	277	8 (5)	169	13 (8)	195	16 (8)	58	24 (9)	225.8	83	0.40	0.17	0.40	0.60

GARS: Groningen Activity Restriction Scale; IQR: Inter Quartile Range (Q3-Q1); NMDIP: neuromuscular disease impact profile; SF-36: Medical Outcome study Short Form Questionnaire.

EFI, NMDIP and GARS scales: higher scores = worse health; – = not statistically significant