Table 3.
Reliability and validity analysis
| Subscale | Number of items | Interclass correlation coefficients (95 % CI) | Cronbach’s alpha (95 % CI) | Range of item-scale correlations | Convergent validity | Discriminant validity |
|---|---|---|---|---|---|---|
| General health | 1 | 0.986 (0.947-0.996) | NA | NA | NA | NA |
| General vision | 1 | 0.808 (0.285-0.948) | NA | NA | NA | NA |
| Ocular pain | 2 | 0.941 (0.780-0.984) | 0.746 (0.626-0.827) | 0.886-0.900 | 100 | 100 |
| Near activities | 3 | 0.958 (0.844-0.989) | 0.827 (0.760-0.878) | 0.816-0.897 | 100 | 100 |
| Distance activities | 3 | 0.947 (0.803-0.986) | 0.785 (0.679-0.860) | 0.799-0.850 | 100 | 100 |
| Social functioning | 2 | 0.968 (0.880-0.991) | 0.643 (0.467-0.761) | 0.870-0.877 | 100 | 100 |
| Mental health | 4 | 0.904 (0.645-0.974) | 0.728 (0.630-0.804) | 0.599-0.872 | 100 | 100 |
| Role difficulties | 2 | 0.965 (0.871-0.991) | 0.804 (0.712-0.867) | 0.904-0.927 | 100 | 100 |
| Dependency | 3 | 0.895 (0.610-0.972) | 0.824 (0.756-0.875) | 0.740-0.907 | 100 | 100 |
| Driving | 3 | NA | 0.889 (0.787-0.947) | 0.898-0.964 | 100 | 100 |
| Color vision | 1 | 0.933 (0.752-0.982) | NA | NA | NA | NA |
| Peripheral vision | 1 | 0.964 (0.865-0.990) | NA | NA | NA | NA |
NA- not applicable (needs two or more items), CI confidence interval