Validation of a proposed WOMAC short form for patients with hip osteoarthritis

Table 3 Severity levels, standard errors, and goodness of fit indices of the pain and function short scales with application of the Rasch model in both cohorts

Items*	Item description	Cohort 1 (n = 788)					Cohort 2 (n = 445)
		δ (logit)	SE	Infit MNSQ	Outfit MNSQ	Rank based on logit	δ (logit)	SE	Infit MNSQ	Outfit MNSQ	Rank based on logit
Pain^†
Item 4	Sitting or lying	2.21	0.07	1.33	1.32	1	2.30	0.09	1.30	1.29	1
Item 1	Walking on flat surface	-0.15	0.07	0.76	0.75	2	-0.07	0.09	0.84	0.87	2
Item 2	Up/down stairs	-2.06	0.07	0.88	0.89	3	-2.23	0.09	0.79	0.79	3
Function^‡
Item 6	Walking on flat surface	1.42	0.05	0.88	0.89	1	1.34	0.07	0.87	0.87	1
Item 15	Getting on/off toilet	0.83	0.05	1.15	1.14	2	0.96	0.07	1.16	1.15	2
Item 1	Descending stairs	0.63	0.05	1.01	0.99	3	0.37	0.07	1.00	0.97	3
Item 8	Shopping	0.01	0.06	1.07	1.04	4	0.01	0.08	1.08	1.04	4
Item 3	Rising from sitting	-0.15	0.06	0.93	0.95	5	-0.01	0.08	0.96	1.00	5
Item 2	Ascending stairs	-0.25	0.06	0.86	0.85	6	-0.36	0.08	0.84	0.79	6
Item 7	Getting in/out of car	-0.96	0.06	0.84	0.81	7	-0.91	0.08	0.85	0.82	7
Item 9	Putting on socks	-1.53	0.06	1.30	1.17	8	-1.41	0.09	1.32	1.22	8

*Items are referred to by the original name in the WOMAC long form.
^†Cohort 1: person separation index = 1.55; item separation index = 24.98; cohort 2: person separation index = 1.56; item separation index = 19.44.
^‡Cohort 1: person separation index = 2.25; item separation index = 15.39; cohort 2: person separation index = 2.21; item separation index = 10.44.
δ = level of severity (higher values indicate higher severity); SE = standard error; MNSQ = mean square fit statistic.

ISSN: 1477-7525