Table 2. Characteristics of study population according to different economic groups and study phases, Shahroud, Iran .
| Variables | Economic status in first phase of study in 2009 | |||||||
| Low | Moderate | High | p | |||||
| Mean/n | SD/Proportion | Mean/n | SD/Proportion | Mean/n | SD/Proportion | |||
| Gender (Female) | 934 | 68.4 | 845 | 59.0 | 1251 | 52.7 | <0.001b | |
| Age (Year) | 52.2 | 6.5 | 51.5 | 6.4 | 49.8 | 5.7 | <0.001c | |
| Having cataract (Grade>=2) | 52 | 3.8 | 46 | 3.2 | 39 | 1.6 | <0.001b | |
| Diabetes (Yes) | 201 | 14.7 | 169 | 11.8 | 267 | 11.2 | <0.001b | |
| Hypertension (Yes) | 506 | 37.0 | 539 | 37.6 | 930 | 39.2 | 0.375 | |
| Smoking (Yes) | 162 | 11.8 | 194 | 13.5 | 290 | 12.2 | 0.347b | |
| Supplementary Insurance (Yes) | 362 | 30.0 | 511 | 39.4 | 1194 | 53.9 | <0.001b | |
| Education (Year) | 4.3 | 3.8 | 6.1 | 3.9 | 9.5 | 4.3 | <0.001c | |
| Variables | Economic status in second phase of study in 2014 | |||||||
| Low | Moderate | High | p | |||||
| Mean/n | SD/Proportion | Mean/n | SD/Proportion | Mean/n | SD/Proportion | |||
| Gender (Female) | 1056 | 67.6 | 917 | 59.0 | 807 | 50.6 | <0.001a | |
| Age (Year) | 57.7 | 6.5 | 55.5 | 6.0 | 54.3 | 5.6 | <0.001b | |
| Having cataract (Grade>=2) | 429 | 27.4 | 286 | 18.3 | 168 | 10.5 | <0.001a | |
| Diabetes (Yes) | 416 | 26.8 | 370 | 23.9 | 332 | 20.9 | <0.001a | |
| Hypertension (Yes) | 1045 | 66.8 | 948 | 60.9 | 915 | 57.2 | <0.001 | |
| Smoking (Yes) | 192 | 12.2 | 220 | 14.1 | 262 | 16.4 | 0.006a | |
| Supplementary Insurance (Yes) | 755 | 48.3 | 877 | 56.3 | 1018 | 63.7 | <0.001a | |
| Education (Year) | 4.4 | 3.7 | 7.1 | 4.0 | 10.2 | 4.2 | <0.001b | |
SD: Standard Deviation; BMI:Body Mass Index;aChi- squared test, bKruskal Wallis test