Table 2.
Reliability and validity analysis of the NEI VFQ‐25 and VF‐14 using classical test theory.
| Index (item number of subscale) | Score (mean ± SD) | Cronbach's α | Average item–total score correlation | Floor responses (%) | Ceiling responses (%) |
|---|---|---|---|---|---|
| VF‐14 | 46.5 ± 15.0 | 0.95 | 0.709 | 0.9 | 0.1 |
| NEI VFQ‐25 | 76.1 ± 19.0 | 0.89 | 0.734 | 0.0 | 0.1 |
| General health (1) | 39.4 ± 19.7 | NA | NA | 6.6 | 1.0 |
| General vision (1) | 45.5 ± 16.8 | NA | NA | 0.2 | 0.1 |
| Ocular pain (2) | 85.5 ± 20.8 | 0.67 | 0.860 | 0.3 | 56.3 |
| Near activities (3) | 67.5 ± 24.7 | 0.80 | 0.738 | 1.4 | 14.2 |
| Distance activities (3) | 77.6 ± 23.7 | 0.90 | 0.762 | 0.8 | 36.9 |
| Social functioning (2) | 86.8 ± 22.3 | 0.89 | 0.823 | 1.1 | 63.5 |
| Mental health (4) | 78.7 ± 24.9 | 0.88 | 0.772 | 0.9 | 35.2 |
| Role difficulties (2) | 71.8 ± 29.5 | 0.93 | 0.932 | 1.7 | 44.6 |
| Dependency (3) | 81.0 ± 27.2 | 0.93 | 0.942 | 1.1 | 59.0 |
| Driving* (3) | 73.4 ± 35.1 | 0.77 | 0.744 | 12.2 | 49.1 |
| Colour vision (1) | 88.4 ± 22.8 | NA | NA | 1.7 | 73.0 |
| Peripheral vision (1) | 81.1 ± 23.7 | NA | NA | 0.6 | 51.5 |
NA = not applicable (statistics need two or more items), NEI VFQ‐25 = National Eye Institute Visual Functioning Questionnaire, SD = standard deviation, VF‐14 = Visual Function Index.
*
287 samples in the ‘Driving’ subscale due to missing responses (not driving for other reasons).