Table 4: Internal Validity of Studies.
| Study | Sampling Method | Sample Size Calculation a priori | Standardized measurements | Reliability Assessments |
|---|---|---|---|---|
| Chennai Glaucoma Study Southern India (36) |
Multistage sampling | Yes | Yes | Inter-rater reliability |
| Aravind Comprehensive Eye survey Southern India (5) |
3 stage cluster sampling |
Not reported | Yes | Study ophthalmologists were standardized to each other and to a senior ophthalmologist considered the reference standard. Standardization was repeated during the study. |
| Blue Mountains Study Australia(37-39) |
census | Not reported | Yes | Inter- and Intra-rater reliability |
| Barbados Eye Study Barbados, West Indies(35;40;41) |
Simple Random Sampling |
Not reported | Yes | Inter- and intra-rater reliability |
| Baltimore Eye Study USA(42;43) |
Stratified Multistage sampling |
Not reported | Yes | Intra-rater reliability |
| Beaver Dam Study USA (44;45) |
census | Not reported | Yes | Consensus of ¾ raters on 94.8% of visual field tests. |