Risk factor value, x | Population A, without intervention | Population B, with intervention | Odds ratio | ||||
r | n | Risk estimate* | r | n | Risk estimate* | ||
1 | 10 | 100 | 0.1 | 10 | 200 | 0.05 | 0.47 |
2 | 60 | 300 | 0.2 | 45 | 300 | 0.15 | 0.71 |
3 | 180 | 600 | 0.3 | 125 | 500 | 0.25 | 0.77 |
All levels | 250 | 1000 | 0.25 | 180 | 1000 | 0.18 | 0.66 |
*Note that the risks in population A if they had had the intervention would be half the observed estimates, and in population B if they had not had the intervention would be twice the observed estimate.