Standardizing disease-specific quality of life measures across multiple chronic conditions: development and initial evaluation of the QOL Disease Impact Scale (QDIS®)

Table 3 Summary of item-level CFA and IRT evaluations by disease group and all diseases combined and disease-specific versus standardized inter-scale correlations^a

Disease	Confirmatory Factor Analysis						IRT parameters		Item r with theta score^d	Inter-scale correlations^e
Disease	Χ²	df	CFI	RMSEA (90 % CI)	Factor Loadings^b	Residuals^c	Slopes	Thresholds	Item r with theta score^d	Inter-scale correlations^e
Arthritis	7037	1127	0.979	0.077	0.91	0.026	2.58	0.99	0.76	0.9996
Arthritis	7037	1127	0.979	(0.076–0.079)	0.74–0.94	0.00–0.143	1.18–4.02	−0.83–2.72	0.59–0.86	0.9996
CKD	1865	1127	0.991	0.058	0.93	0.026	3.55	1.36	0.76	0.9983
CKD	1865	1127	0.991	(0.053–0.062)	0.76–0.97	0.00–0.202	1.29–5.94	−0.24–2.38	0.62–0.83	0.9983
Cardiovascular	3658	1127	0.987	0.069	0.92	0.022	3.13	1.18	0.75	0.9998
Cardiovascular	3658	1127	0.987	(0.067–0.072)	0.81–0.96	0.00–0.141	1.62–5.51	−0.20–2.71	0.59–0.86	0.9998
Diabetes	3991	1127	0.985	0.061	0.91	0.027	2.98	1.85	0.70	0.9992
Diabetes	3991	1127	0.985	(0.059–0.063)	0.81–0.97	0.00–0.186	1.36–6.05	−0.29–2.99	0.51–0.81	0.9992
Respiratory	4847	1127	0.990	0.060	0.92	0.021	3.13	1.50	0.75	0.9999
Respiratory	4847	1127	0.990	(0.058–0.061)	0.84–0.97	0.00–0.124	1.64–5.87	0.10–2.67	0.58–0.86	0.9999
Combined	20,669	1127	0.982	0.074	0.92	0.023	3.05	1.34	0.74	-
Combined	20,669	1127	0.982	(0.073,0.075)	0.81–0.96	0.00–0.158	1.49–5.30	−0.10–2.60	0.58–0.85	-

Abbreviations: Χ ² chi-square test of model fit, df degrees of freedom, CFI comparative fit index, RMSEA root mean square error of approximation, CKD chronic kidney disease
^aAll entries are median on first line and minimum-maximum on second line unless noted
^bLoadings from the completely standardized CFA solution for each disease (rows 1–5) or all diseases combined (row 6)
^cAbsolute value of residual correlations after controlling for single factor for each disease (rows 1–5) or all diseases combined (row 6)
^dCorrelation between person-level item scores and total bank theta scores for each disease (rows 1–5) or all diseases combined (row 6)
^eCorrelation between person-level total bank theta scores estimated using disease-specific and standardized item parameters

ISSN: 1477-7525