Box 1. Calculating incidence measures of occurrence in the GATE frame
| Incidence | = (number of people developing an outcome ÷ the number in a population) during time T |
| Exposure group occurrence [EGO] or experimental event rate [EER] | |
| = a ÷ E during time T = a ÷ (a+c) during time T = (a ÷ (a+c))/T | |
| Example: Incidence of CHD death in HRT group from HERS3 | |
| EGO (or EER) | |
| = [71 events ÷ 1380 women] over 4.1 years = 51.5 events per 1000 women over 4.1 years = 12.5 events per 1000 women per year | |
| Comparison group occurrence [CGO] or control event rate [CER] | |
| = b ÷ C during time T = b ÷ (b+d) during time T = (b ÷ (b+d))/T | |
| Example: Incidence of CHD death in placebo group from HERS3 | |
| CGO (or CER) | |
| = [58 events ÷ 1383 women] over 4.1 years = 41.9 events per 1000 women over 4.1 years = 10.2 events per 1000 women per year | |