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Illustration of the effect of collapsing exposure categories
| X1=1 | X1=2 | ||||||||
|---|---|---|---|---|---|---|---|---|---|
| X 2 | Diseased | Not diseased | Total | RR | X 2 | Diseased | Not diseased | Total | RR |
| 1 | 20 | 380 | 400 | 1.0 | 1 | 5 | 95 | 100 | 1.0 |
| 2 | 30 | 270 | 300 | 2.0 | 2 | 20 | 180 | 200 | 2.0 |
| 3 | 30 | 170 | 200 | 3.0 | 3 | 45 | 255 | 300 | 3.0 |
| 4 | 20 | 80 | 100 | 4.0 | 4 | 80 | 320 | 400 | 4.0 |
The table gives the true situation
