A Revised Version of Diabetes Quality of Life Instrument Maintaining Domains for Satisfaction, Impact, and Worry

Table 3

Summary of statistics for item and person parameters and unidimensionality using the principal component analysis (PCA) of the DQoL by Rasch analysis.

Domain	Number of items	Item^a		Person^a		Cronbach’s alpha	Variance in data explained by measures		Unexplained variance in contrast 1 of PCA of residuals (eigenvalue)
		Separation index	Reliability	Separation index	Reliability		Empirical	Modelled
Original version
Satisfaction	15	6.01	0.97	2.91	0.89	0.95	55.4%	55.8%	7.7% (2.6)
Impact	20	11.58	0.99	1.69	0.74	0.85	39.7%	43.1%	8.1% (2.7)
Worry	11	12.44	0.99	1.72	0.75	0.85	48.3%	54.0%	17.8% (3.8)
Simplified/revised version
Satisfaction	6	3.44	0.92	2.27	0.84	0.93	63.3%	63.5%	9.8% (1.6)
Impact	4	7.27	0.98	1.22	0.60	0.79	51.9%	52.4%	19.0% (1.6)
Worry	3	10.16	0.99	1.14	0.57	0.75	62.6%	62.4%	20.6% (1.7)

^aSummary of nonextreme measured person/item. An acceptable value for reliability is >0.7, while for separation indices is >2.0. The variance explained by the measures for the empirical calculation was almost identical to the model and >40%, and the unexplained variance explained by the first contrast < 15% (eigenvalue < 2.0) suggests unidimensionality of the scale.