Table 5

Fit statistics after adjustment for cross-cultural DIF in the affected testlets

Domain	Testlet	Location	SE	Fit residuals	χ²	p Value
AS
Pain	Pain–Norway	−0.15	0.03	−1.13	7.76	0.56
Pain	Pain-–Others	−0.01	0.01	0.47	14.70	0.10
Movement	Movement	0.07	0.01	−0.80	10.73	0.29
Feelings	Feelings	0.04	0.01	−0.18	16.08	0.07
Disease process	Disease process	−0.14	0.01	0.21	8.11	0.52
Treatments	Treatments	0.04	0.01	0.83	7.97	0.54
Self-help	Self-help	−0.10	0.01	2.04	5.59	0.78
Support	Support –The Netherlands	0.15	0.04	−0.96	7.18	0.62
Support	Support–Others	0.09	0.01	0.70	10.02	0.35
PsA
Pain	Pain–Austria	−0.06	0.03	−1.07	6.73	0.46
	Pain–Norway	−0.70	0.04	0.23	6.54	0.48
	Pain–The Netherlands	0.13	0.03	−0.09	5.69	0.58
	Pain–Others	0.08	0.02	−0.57	5.65	0.58
Movement	Movement	0.20	0.01	2.51	8.28	0.31
Feelings	Feelings	0.16	0.01	2.45	4.09	0.77
Disease process	Disease process–Finland	−0.15	0.04	−1.93	4.71	0.70
Disease process	Disease process–Others	−0.13	0.01	−0.11	4.99	0.66
Treatments	Treatments–The Netherlands	−0.08	0.03	0.77	8.07	0.33
Treatments	Treatments–Sweden	−0.05	0.03	1.35	5.09	0.65
	Treatments–Others	0.14	0.01	−0.27	7.72	0.36
Self-help	Self-help–The Netherlands	−0.22	0.03	2.54	17.90	0.01
	Self-help–Portugal	0.16	0.03	0.38	3.55	0.83
	Self-help–Others	−0.05	0.01	0.37	9.73	0.20
Support	Support–Austria	0.49	0.03	1.37	4.74	0.69
	Support-–Finland	−0.40	0.05	−0.93	6.53	0.48
	Support–Portugal	0.21	0.03	0.87	5.68	0.58
	Support–Others	0.25	0.02	0.44	8.69	0.28
SSc
Pain	Pain	0.06	0.02	0.17	6.93	0.23
Movements	Movements	0.12	0.02	−0.99	8.34	0.14
Feelings	Feelings	0.09	0.02	1.79	3.37	0.64
Disease process	Disease process	−0.21	0.02	−0.02	10.97	0.05
Treatments	Treatments–The Netherlands	−0.06	0.03	1.96	3.50	0.62
Treatments	Treatments–Others	0.03	0.02	0.74	5.61	0.35
Self-help	Self-help	−0.16	0.02	0.77	4.13	0.53
Support	Support–The Netherlands	0.22	0.04	1.23	3.62	0.61
Support	Support–Others	−0.09	0.03	1.28	10.51	0.06
SLE
Pain	Pain	0.01	0.02	−0.13	5.31	0.50
Movement	Movements–Spain	0.03	0.03	−0.43	4.41	0.62
Movement	Movements–Others	0.06	0.02	0.05	2.28	0.89
Feelings	Feelings	−0.04	0.02	2.16	5.56	0.47
Disease process	Disease process	−0.18	0.01	−0.60	12.62	0.05
Treatments	Treatments–Spain	0.18	0.02	0.27	4.02	0.67
Treatments	Treatments–Others	−0.02	0.02	0.75	4.23	0.65
Self-help	Self-help	−0.12	0.02	0.18	6.20	0.40
Support	Support	0.08	0.02	2.05	9.22	0.16
FMS
Pain	Pain	−0.04	0.02	0.40	5.38	0.37
Movements	Movements	−0.04	0.02	0.68	3.56	0.61
Feelings	Feelings	−0.05	0.02	0.79	3.20	0.67
Disease process	Disease process	−0.13	0.02	−1.24	6.88	0.23
Treatments	Treatments	0.28	0.02	1.96	5.52	0.36
Self-help	Self-help	−0.08	0.02	0.13	8.72	0.12
Support	Support–The Netherlands	0.06	0.02	−0.14	6.12	0.29

AS, ankylosing spondylitis; DIF, differential item functioning; FMS, fibromyalgia syndrome; p, Bonferroni-adjusted χ² probability (non-significant p=Fit to the model); PsA, psoriatic arthritis; SLE, systemic lupus erythematosus; SSc, systemic sclerosis.