A rare disease patient-reported outcome measure: revision and validation of the German version of the Systemic Sclerosis Quality of Life Questionnaire (SScQoL) using the Rasch model

Table 3 Summary fit statistics

Analysis	Item Fit Residual		Person Fit Residual		Chi Square Interaction				Unidimensionality
Analysis	Mean	SD	Mean	SD	Value (df)	p	PSI	N	Independent t-tests (95% CI)
Individual items	− 0.0849	1.1739	− 0.19	1.313	51.2238	0.0066	0.990	77	0.256 (0.208 to 0.305)
Five domains	0.1019	0.9283	− 0.25	0.917	5.3426	0.3755	0.915	77	0.0649 (0.016 to 0.114)
Model fit	0	1	0	1		> *0.05*	> 0.7		Lower bound 95%CI < 0.05

ISSN: 1750-1172