Scoring and psychometric properties of the Eye-Drop Satisfaction Questionnaire (EDSQ), an instrument to assess satisfaction and compliance with glaucoma treatment

Table 2 Item convergent and discriminant validity, internal consistency reliability, and floor and ceiling effect obtained using the hypothesized and exploratory structures of the EDSQ - Patients with complete EDSQ data (N = 145)

Dimensions	No. of items	Range of item-scale correlations	Item convergent validity^a (% success)	Item discriminant validity^b (% success)	Cronbach's alpha	Floor (%)	Ceiling (%)
*Hypothesized structure resulting from the development phase*
Apprehension	3	0.42-0.54	100.0	100.0	0.66	28.3	0.0
Patient-clinician relationship	5	0.10-0.68	80.0	88.0	0.65	0.0	1.4
Patient experience	7	0.12-0.62	57.1	80.0	0.73	0.7	0.0
Patient knowledge	3	0.42-0.53	100.0	93.3	0.70	0.0	30.3
Patient-treatment interaction	6	0.08-0.51	33.3	76.7	0.56	0.0	6.9
Travel	3	0.00-0.46	66.7	66.7	0.38	5.5	0.0
*Exploratory structure resulting from the PCA*
Concern about treatment	5	0.45-0.64	100.0	100.0	0.78	18.9	0.0
Concern about disease	2	0.82-0.82	100.0	100.0	0.90	8.8	5.4
Satisfaction with patient-clinician relationship	5	0.49-0.73	100.0	100.0	0.78	0.0	20.9
Positive beliefs	3	0.49-0.67	100.0	93.3	0.74	0.0	4.7
Treatment convenience	3	0.50-0.60	100.0	100.0	0.72	0.7	13.5
Self-declared compliance	3	0.36-0.46	66.7	100.0	0.65	0.0	49.3

PCA, Principal Component Analysis
^aSuccess criteria: item-scale correlation greater than 0.4.
^bFor each item, correlation coefficient with its own scale is compared with correlation coefficients with the other scales. Reported is the percentage of all pairwise comparisons where the correlation of an item with its own scale is greater than correlation with the other scale.

ISSN: 1471-2415