Table 8.

Overall performance of the NEI VFQ-25

Parametar	NEI VFQ-25
Misfitting items (n)	5
Person separation reliability (PSR)	0.91
Person separation index (PSI)	3.26
Principal component analysis (eigenvalue in 1st contrast)	3.3
Valid subscales (n)	3
DIF by age (2 items)	≤0.61 logits
DIF by sex (3 items)	≤0.61 logits
DIF by systemic comorbidity (1 item)	0.94 logits
DIF by better eye visual acuity (5 items)	≤0.87 logits